Fail to execute model without aird for languages with inheritance

In the offical example SequentialFSM,
if we create a launch configuration that doesn't specify the animation aird, then the execution fails with an exception in the model loader

```
54582462 [Worker-48] ERROR fr.inria.diverse.melange.resource.MelangeDerivedStateComputer - Fatal exception
java.lang.NullPointerException
at fr.inria.diverse.melange.utils.EPackageProvider.getPackages(EPackageProvider.java:89)
at fr.inria.diverse.melange.utils.EPackageProvider$1.apply(EPackageProvider.java:138)
at fr.inria.diverse.melange.utils.EPackageProvider$1.apply(EPackageProvider.java:1)
at org.eclipse.xtext.xbase.lib.internal.FunctionDelegate.apply(FunctionDelegate.java:42)
at com.google.common.collect.Iterators$8.transform(Iterators.java:794)
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48)
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48)
at com.google.common.collect.Iterators$5.hasNext(Iterators.java:543)
at com.google.common.collect.AbstractMultimap.putAll(AbstractMultimap.java:82)
at com.google.common.collect.HashMultimap.putAll(HashMultimap.java:49)
at fr.inria.diverse.melange.utils.EPackageProvider.getPackages(EPackageProvider.java:165)
at fr.inria.diverse.melange.ast.ModelingElementExtensions.getPkgs(ModelingElementExtensions.java:93)
at fr.inria.diverse.melange.ast.LanguageExtensions.isTypable(LanguageExtensions.java:293)
at fr.inria.diverse.melange.ast.ModelTypeExtensions.isComparable(ModelTypeExtensions.java:424)
at fr.inria.diverse.melange.processors.TypingInferrer$5.apply(TypingInferrer.java:109)
at fr.inria.diverse.melange.processors.TypingInferrer$5.apply(TypingInferrer.java:1)
at org.eclipse.xtext.xbase.lib.internal.BooleanFunctionDelegate.apply(BooleanFunctionDelegate.java:41)
at com.google.common.collect.Iterators$7.computeNext(Iterators.java:647)
at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:143)
at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:138)
at java.lang.Iterable.forEach(Iterable.java:74)
at fr.inria.diverse.melange.processors.TypingInferrer._preProcess(TypingInferrer.java:179)
at fr.inria.diverse.melange.processors.TypingInferrer.preProcess(TypingInferrer.java:205)
at fr.inria.diverse.melange.resource.MelangeDerivedStateComputer$1.accept(MelangeDerivedStateComputer.java:111)
at fr.inria.diverse.melange.resource.MelangeDerivedStateComputer$1.accept(MelangeDerivedStateComputer.java:1)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at fr.inria.diverse.melange.resource.MelangeDerivedStateComputer.installDerivedState(MelangeDerivedStateComputer.java:115)
at org.eclipse.xtext.resource.DerivedStateAwareResource.installDerivedState(DerivedStateAwareResource.java:242)
at org.eclipse.xtext.xbase.resource.BatchLinkableResource.getContents(BatchLinkableResource.java:148)
at fr.inria.diverse.melange.resource.MelangeResourceImpl.getXmofURI(MelangeResourceImpl.java:457)
at fr.inria.diverse.melange.resource.MelangeResourceImpl.adaptResourceToLang(MelangeResourceImpl.java:308)
at fr.inria.diverse.melange.resource.MelangeResourceImpl.doAdapt(MelangeResourceImpl.java:487)
at fr.inria.diverse.melange.resource.MelangeResourceImpl.eAdapters(MelangeResourceImpl.java:538)
at org.eclipse.xtext.resource.XtextResourceSet$ResourcesList.inverseAdd(XtextResourceSet.java:151)
at org.eclipse.xtext.resource.XtextResourceSet$ResourcesList.inverseAdd(XtextResourceSet.java:1)
at org.eclipse.emf.common.notify.impl.NotifyingListImpl.addUnique(NotifyingListImpl.java:312)
at org.eclipse.emf.common.util.AbstractEList.add(AbstractEList.java:303)
at org.eclipse.emf.ecore.resource.impl.ResourceSetImpl.createResource(ResourceSetImpl.java:435)
at org.eclipse.emf.ecore.resource.impl.ResourceSetImpl.createResource(ResourceSetImpl.java:423)
at org.eclipse.gemoc.executionframework.extensions.sirius.modelloader.DefaultModelLoader.loadModel(DefaultModelLoader.java:185)
at org.eclipse.gemoc.executionframework.extensions.sirius.modelloader.DefaultModelLoader.loadModel(DefaultModelLoader.java:114)
at org.eclipse.gemoc.executionframework.engine.commons.ModelExecutionContext.initializeResourceModel(ModelExecutionContext.java:73)
at org.eclipse.gemoc.execution.sequential.javaengine.ui.launcher.Launcher.createExecutionEngine(Launcher.java:64)
at org.eclipse.gemoc.executionframework.engine.ui.launcher.AbstractSequentialGemocLauncher.launch(AbstractSequentialGemocLauncher.java:106)
at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:885)

```

additionnally, after such failure, when trying to create the missing aird, in a new representation file (aird), the model may stay in a strange state where Sirius fails to associate the view point to the model with the following exception

```
!ENTRY org.eclipse.sirius.ui 4 0 2017-09-15 09:23:01.849
!MESSAGE Error creating Representations File
!STACK 0
java.lang.NullPointerException
at org.eclipse.gemoc.executionframework.extensions.sirius.modelloader.DebugPermissionAuthority.canEditInstance(DebugPermissionAuthority.java:58)
at org.eclipse.sirius.ecore.extender.business.internal.permission.ReadOnlyWrapperPermissionAuthority.canEditInstance(ReadOnlyWrapperPermissionAuthority.java:95)
at org.eclipse.sirius.diagram.business.internal.experimental.sync.DDiagramSynchronizer.refreshOperation(DDiagramSynchronizer.java:370)
at org.eclipse.sirius.diagram.business.internal.experimental.sync.DDiagramSynchronizer.refresh(DDiagramSynchronizer.java:356)
at org.eclipse.sirius.diagram.business.internal.sync.DDiagramSynchronizer.refresh(DDiagramSynchronizer.java:91)
at org.eclipse.sirius.diagram.business.internal.dialect.DiagramDialectServices.refresh(DiagramDialectServices.java:271)
at org.eclipse.sirius.business.internal.dialect.DialectManagerImpl.refresh(DialectManagerImpl.java:115)
at org.eclipse.sirius.business.internal.dialect.DialectManagerImpl.refresh(DialectManagerImpl.java:106)
at org.eclipse.sirius.diagram.business.internal.dialect.DiagramDialectServices.createRepresentation(DiagramDialectServices.java:193)
at org.eclipse.sirius.business.internal.dialect.DialectManagerImpl.createRepresentation(DialectManagerImpl.java:153)
at org.eclipse.sirius.diagram.tools.api.command.view.CreateDiagramWithInitialOperation.execute(CreateDiagramWithInitialOperation.java:98)
at org.eclipse.sirius.business.api.helper.task.TaskExecutor.execute(TaskExecutor.java:64)
at org.eclipse.sirius.tools.api.command.SiriusCommand.doExecute(SiriusCommand.java:80)
at org.eclipse.emf.transaction.RecordingCommand.execute(RecordingCommand.java:135)
at org.eclipse.emf.workspace.EMFCommandOperation.doExecute(EMFCommandOperation.java:119)
at org.eclipse.emf.workspace.AbstractEMFOperation.execute(AbstractEMFOperation.java:150)
at org.eclipse.core.commands.operations.DefaultOperationHistory.execute(DefaultOperationHistory.java:488)
at org.eclipse.emf.workspace.impl.WorkspaceCommandStackImpl.doExecute(WorkspaceCommandStackImpl.java:208)
at org.eclipse.emf.transaction.impl.AbstractTransactionalCommandStack.execute(AbstractTransactionalCommandStack.java:165)
at org.eclipse.emf.transaction.impl.AbstractTransactionalCommandStack.execute(AbstractTransactionalCommandStack.java:219)
at org.eclipse.sirius.diagram.business.internal.dialect.DiagramDialectServices.initRepresentationForElement(DiagramDialectServices.java:354)
at org.eclipse.sirius.business.api.dialect.AbstractRepresentationDialectServices.initRepresentations(AbstractRepresentationDialectServices.java:546)
at org.eclipse.sirius.business.api.dialect.AbstractRepresentationDialectServices.initRepresentations(AbstractRepresentationDialectServices.java:497)
at org.eclipse.sirius.diagram.business.internal.dialect.DiagramDialectServices.initRepresentations(DiagramDialectServices.java:334)
at org.eclipse.sirius.business.internal.dialect.DialectManagerImpl.initRepresentations(DialectManagerImpl.java:360)
at org.eclipse.sirius.business.internal.session.danalysis.DViewOperations.createView(DViewOperations.java:128)
at org.eclipse.sirius.business.internal.session.danalysis.DAnalysisSessionImpl.createView(DAnalysisSessionImpl.java:1139)
at org.eclipse.sirius.business.api.session.ViewpointSelector.selectViewpoint(ViewpointSelector.java:79)
at org.eclipse.sirius.ui.business.api.viewpoint.ViewpointSelectionCallback.selectViewpoint(ViewpointSelectionCallback.java:40)
at org.eclipse.sirius.ui.business.internal.commands.ChangeViewpointSelectionCommand.doExecute(ChangeViewpointSelectionCommand.java:112)
at org.eclipse.emf.transaction.RecordingCommand.execute(RecordingCommand.java:135)
at org.eclipse.emf.workspace.EMFCommandOperation.doExecute(EMFCommandOperation.java:119)
at org.eclipse.emf.workspace.AbstractEMFOperation.execute(AbstractEMFOperation.java:150)
at org.eclipse.core.commands.operations.DefaultOperationHistory.execute(DefaultOperationHistory.java:488)
at org.eclipse.emf.workspace.impl.WorkspaceCommandStackImpl.doExecute(WorkspaceCommandStackImpl.java:208)
at org.eclipse.emf.transaction.impl.AbstractTransactionalCommandStack.execute(AbstractTransactionalCommandStack.java:165)
at org.eclipse.emf.transaction.impl.AbstractTransactionalCommandStack.execute(AbstractTransactionalCommandStack.java:219)
at org.eclipse.sirius.ui.business.api.viewpoint.ViewpointSelection$8.run(ViewpointSelection.java:489)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:119)

```

In order to successfully be able to add the view points and patch the launch configuation, we need, at minimum, to close and re-open the project containing the model (or more radically, restart eclipse :wink: )

steps to reproduce the issue:
- install fsm example language and model in their respective workbenches
- in the modeling workbench, copy a model that usually work (only the .fsm) create a launch configuration for it without specifying the aird.
- launch the model (debug mode) -> crash
- then right click on the fsm and try to create a representation and select the FSM and XFSM view points.