Live migrate VM failed when 'Error-ed" VM snapshots exists and VM stopped.

### problem

Live migrate VM failed when 'Error-ed" VM snapshots exists and VM stopped.

```
2026-04-10 08:06:55,931 DEBUG [c.c.a.m.ClusteredAgentAttache] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Seq 1-5825124643027026430: Routed from 32986137363417
2026-04-10 08:06:55,933 DEBUG [c.c.a.t.Request] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Seq 1-5825124643027026430: Sending { Cmd , MgmtId: 32986137363417, via: 1(ref-trl-11538-k-Mol8-suresh-anaparti-kvm1), Ver: v1, Flags: 100011, [{"com.cloud.agent.api.RestoreVMSnapshotCommand":{"snapshots":[{"id":"1","snapshotName":"i-2-3-VM_VS_20260410080110","type":"DiskAndMemory","createTime":"1775808070000","quiescevm":"true"}],"snapshotAndParents":{},"volumeTOs":[{"uuid":"4fbf60a0-9ecb-4fa5-8238-35363309b8fe","volumeType":"ROOT","dataStore":{"org.apache.cloudstack.storage.to.PrimaryDataStoreTO":{"uuid":"d90d639c-b4df-387d-a3cc-c4a9fad1a939","name":"ref-trl-11538-k-Mol8-suresh-anaparti-kvm-pri2","id":"2","poolType":"NetworkFilesystem","host":"10.0.32.4","path":"/acs/primary/ref-trl-11538-k-Mol8-suresh-anaparti/ref-trl-11538-k-Mol8-suresh-anaparti-kvm-pri2","port":"2049","url":"NetworkFilesystem://10.0.32.4/acs/primary/ref-trl-11538-k-Mol8-suresh-anaparti/ref-trl-11538-k-Mol8-suresh-anaparti-kvm-pri2/?ROLE=Primary&STOREUUID=d90d639c-b4df-387d-a3cc-c4a9fad1a939","isManaged":"false"}},"name":"ROOT-3","size":"(8.00 GB) 8589934592","path":"4fbf60a0-9ecb-4fa5-8238-35363309b8fe","volumeId":"3","vmName":"i-2-3-VM","accountId":"2","format":"QCOW2","provisioningType":"THIN","poolId":"2","id":"3","deviceId":"0","hypervisorType":"KVM","directDownload":"false","deployAsIs":"false","followRedirects":"false"},{"uuid":"f98a16a9-d53a-4c32-b1c4-f20340435757","volumeType":"DATADISK","dataStore":{"org.apache.cloudstack.storage.to.PrimaryDataStoreTO":{"uuid":"c3812f1e-6c98-408b-80bf-8c294ecef883","name":"pflexcspool1","id":"5","poolType":"PowerFlex","host":"10.0.32.170","path":"3357f56800000000","port":"0","url":"PowerFlex://10.0.32.170/3357f56800000000/?ROLE=Primary&STOREUUID=c3812f1e-6c98-408b-80bf-8c294ecef883","isManaged":"true"}},"name":"MyDATA01","size":"(8.00 GB) 8589934592","path":"8a4d19710000005a:vol-20-2f1e-7565","volumeId":"20","vmName":"i-2-3-VM","accountId":"2","format":"QCOW2","provisioningType":"THIN","poolId":"5","id":"20","deviceId":"1","hypervisorType":"KVM","directDownload":"false","deployAsIs":"false","followRedirects":"false"}],"vmName":"i-2-3-VM","guestOSType":"CentOS 5.5 (64-bit)","wait":"0","bypassHostMaintenance":"false"}}] }
2026-04-10 08:06:55,950 DEBUG [c.c.a.t.Request] (AgentManager-Handler-14:[]) (logid:) Seq 1-5825124643027026430: Processing: { Ans: , MgmtId: 32986137363417, via: 1, Ver: v1, Flags: 10, [{"com.cloud.agent.api.Answer":{"result":"false","details":"java.lang.NullPointerException: Cannot invoke "java.lang.Boolean.booleanValue()" because the return value of "com.cloud.agent.api.VMSnapshotTO.getCurrent()" is null
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRestoreVMSnapshotCommandWrapper.execute(LibvirtRestoreVMSnapshotCommandWrapper.java:69)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRestoreVMSnapshotCommandWrapper.execute(LibvirtRestoreVMSnapshotCommandWrapper.java:39)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRequestWrapper.execute(LibvirtRequestWrapper.java:78)
at com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.executeRequest(LibvirtComputingResource.java:1973)
at com.cloud.agent.Agent.processRequest(Agent.java:778)
at com.cloud.agent.Agent$AgentRequestHandler.doTask(Agent.java:1193)
at com.cloud.utils.nio.Task.call(Task.java:83)
at com.cloud.utils.nio.Task.call(Task.java:29)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)
","wait":"0","bypassHostMaintenance":"false"}}] }
...
2026-04-10 08:06:55,951 INFO [c.c.v.ClusteredVirtualMachineManagerImpl] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Migration was unsuccessful. Cleaning up: VM instance {"id":3,"instanceName":"i-2-3-VM","state":"Running","type":"User","uuid":"7b213c30-2290-4801-beb9-5a70a3b5ce3d"}

2026-04-10 08:06:59,232 DEBUG [c.c.a.t.Request] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Seq 1-5825124643027026433: Sending { Cmd , MgmtId: 32986137363417, via: 1(ref-trl-11538-k-Mol8-suresh-anaparti-kvm1), Ver: v1, Flags: 100011, [{"com.cloud.agent.api.StopCommand":{"isProxy":"false","checkBeforeCleanup":"false","forceStop":"false","vlanToPersistenceMap":{"2671":"true"},"volumesToDisconnect":[],"vmName":"i-2-3-VM","executeInSequence":"false","wait":"0","bypassHostMaintenance":"false"}}] }
2026-04-10 08:06:59,232 WARN [c.c.v.ClusteredVirtualMachineManagerImpl] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Unable to transition to a new state from Running via OperationFailed

2026-04-10 08:06:59,235 INFO [c.c.v.VmWorkJobHandlerProxy] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118, ctx-42e19861]) (logid:bfef3797) Rethrow exception java.lang.ClassCastException: class com.cloud.agent.api.Answer cannot be cast to class com.cloud.agent.api.RestoreVMSnapshotAnswer (com.cloud.agent.api.Answer and com.cloud.agent.api.RestoreVMSnapshotAnswer are in unnamed module of loader 'app')
2026-04-10 08:06:59,235 DEBUG [c.c.v.VmWorkJobDispatcher] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118]) (logid:bfef3797) Done with run of VM work job: com.cloud.vm.VmWorkMigrate for VM 3, job origin: 117
2026-04-10 08:06:59,236 ERROR [c.c.v.VmWorkJobDispatcher] (Work-Job-Executor-35:[ctx-2b815626, job-117/job-118]) (logid:bfef3797) Unable to complete AsyncJob {"accountId":2,"cmd":"com.cloud.vm.VmWorkMigrate","cmdInfo":"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-AAlwcQB-AAk","cmdVersion":0,"completeMsid":null,"created":"Fri Apr 10 08:06:34 UTC 2026","id":118,"initMsid":32986137363417,"instanceId":null,"instanceType":null,"lastPolled":null,"lastUpdated":null,"processStatus":0,"removed":null,"result":null,"resultCode":0,"status":"IN_PROGRESS","userId":2,"uuid":"76ff9b90-ac44-4ed9-89d9-43a3a777b16f"}, job origin: 117 java.lang.ClassCastException: class com.cloud.agent.api.Answer cannot be cast to class com.cloud.agent.api.RestoreVMSnapshotAnswer (com.cloud.agent.api.Answer and com.cloud.agent.api.RestoreVMSnapshotAnswer are in unnamed module of loader 'app')
at com.cloud.vm.VirtualMachineManagerImpl.checkVmOnHost(VirtualMachineManagerImpl.java:2405)
at com.cloud.vm.VirtualMachineManagerImpl.migrate(VirtualMachineManagerImpl.java:2875)
at com.cloud.vm.VirtualMachineManagerImpl.orchestrateMigrate(VirtualMachineManagerImpl.java:2733)
at com.cloud.vm.VirtualMachineManagerImpl.orchestrateMigrate(VirtualMachineManagerImpl.java:5524)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:569)
at com.cloud.vm.VmWorkJobHandlerProxy.handleVmWorkJob(VmWorkJobHandlerProxy.java:102)
at com.cloud.vm.VirtualMachineManagerImpl.handleVmWorkJob(VirtualMachineManagerImpl.java:5621)
at com.cloud.vm.VmWorkJobDispatcher.runJob(VmWorkJobDispatcher.java:99)
at org.apache.cloudstack.framework.jobs.impl.AsyncJobManagerImpl$5.runInContext(AsyncJobManagerImpl.java:661)
at org.apache.cloudstack.managed.context.ManagedContextRunnable$1.run(ManagedContextRunnable.java:49)
at org.apache.cloudstack.managed.context.impl.DefaultManagedContext$1.call(DefaultManagedContext.java:56)
at org.apache.cloudstack.managed.context.impl.DefaultManagedContext.callWithContext(DefaultManagedContext.java:103)
at org.apache.cloudstack.managed.context.impl.DefaultManagedContext.runWithContext(DefaultManagedContext.java:53)
at org.apache.cloudstack.managed.context.ManagedContextRunnable.run(ManagedContextRunnable.java:46)
at org.apache.cloudstack.framework.jobs.impl.AsyncJobManagerImpl$5.run(AsyncJobManagerImpl.java:609)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)
```

### versions

ACS 4.20.3 RC4 + Advanced Zone + KVM hypervisor

### The steps to reproduce the bug

1. Deploy a VM
2. Create VM snapshot (should fail, otherwise update state to Error in DB)
3. Live migrate VM to another host

### What to do about it?

Expecting Live migrate VM to succeed (even when failed/error-ed VM snapshots exists), and VM shouldn't be stopped in case of migration failure.

VMSnapshotTO.getCurrent() が使用されている報告された行の LibvirtRestoreVMSnapshotCommandWrapper.java から開始し、続いて VirtualMachineManagerImpl.checkVmOnHost() と移行のクリーンアップパスを追跡します。失敗した、または Error 状態の VM スナップショットのケースを再現し、移行が失敗した場合でも VM を停止せずにライブマイグレーションが成功することを確認します。

索引モデルが issue の本文から書いたものです。