Crash opening animation assets with Morph Targets

REGRESSION: Yes
WORKING: 3068867
BROKEN: 3069877

Crash occurs when the user opens an animation with Morph Targets in Persona.

1. Open QAGame in editor.
2. In the Content Browser, find the animation TestMorph.
3. Double-click it.

RESULT:

Persona will open and then crash.

UE4Editor_Engine!FAnimationRuntime::AppendActiveMorphTargets() animationruntime.cpp:1426
UE4Editor_Engine!USkeletalMeshComponent::ApplyAnimationCurvesToComponent() skeletalmeshcomponent.cpp:1461
UE4Editor_Engine!UAnimInstance::UpdateCurves() animinstance.cpp:1215
UE4Editor_Engine!USkeletalMeshComponent::PostAnimEvaluation() skeletalmeshcomponent.cpp:1427
UE4Editor_Engine!USkeletalMeshComponent::RefreshBoneTransforms() skeletalmeshcomponent.cpp:1354
UE4Editor_UnrealEd!UDebugSkelMeshComponent::RefreshBoneTransforms() debugskelmeshcomponent.cpp:418
UE4Editor_UnrealEd!FAnimationSequenceThumbnailScene::SetAnimation() thumbnailhelpers.cpp:661
UE4Editor_UnrealEd!UAnimSequenceThumbnailRenderer::Draw() animsequencethumbnailrenderer.cpp:26
UE4Editor_UnrealEd!ThumbnailTools::RenderThumbnail() objecttools.cpp:3827
UE4Editor_UnrealEd!FAssetThumbnailPool::Tick() assetthumbnail.cpp:969
UE4Editor_UnrealEd!FTickableEditorObject::TickObjects() tickableeditorobject.h:17
UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:1181
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() unrealedengine.cpp:371
UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2834
UE4Editor!GuardedMain() launch.cpp:156
UE4Editor!GuardedMainWrapper() launchwindows.cpp:126
UE4Editor!WinMain() launchwindows.cpp:202
UE4Editor!__scrt_common_main_seh() exe_common.inl:264
kernel32!<Unknown>
ntdll!<Unknown>