BindingKeyResolver.consumeAnnotation() should expect null array elements

While checking #2804 I realize that generally callers of `org.eclipse.jdt.internal.compiler.lookup.MethodBinding.getAnnotations()` do expect the resulting array to contain nulls.

I could find only one exception: `BindingKeyResolver.consumeAnnotation()` which could probably throw NPE when an annotation could not be resolved. Most likely this can be triggered via `org.eclipse.jdt.core.dom.CompilationUnitResolver.resolve(ICompilationUnit[], String[], ASTRequestor, int, Map, IJavaProject, WorkingCopyOwner, int, IProgressMonitor)` when passing a binding key for a method which contains an annotation (perhaps the key was obtained while the annotation type was still present).