Assigning APX Cloth asset to material element

When assigning an imported apx file to the clothing drop down under the material element of this imported Skeletal Mesh will result in a crash.

Tested in:

4.11.2 CL-2946394
4.12.3 CL-3013449
Dev-Main CL-3016365

1. Open UE4
2. Import attached FBX skeletal mesh
3. Open the Skeletal Mesh
4. Click "Add APEX Clothing File..." and navigate to users Cloak001.apx file
5. Under the Material Element Clothing assign the imported .apx file

Freq: 3/3

Results: The assigned apx file will cause a crash

Expected: shouldn't crash.

UE4Editor_Core!FDebug::AssertFailed() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:440]
UE4Editor_Engine!FSharedPoolPolicyData::GetPoolBucketIndex() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\engine\private\gpuskinvertexfactory.cpp:74]
UE4Editor_Engine!FGPUBaseSkinAPEXClothVertexFactory::ClothShaderType::UpdateClothSimulData() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\engine\private\gpuskinvertexfactory.cpp:876]
UE4Editor_Engine!FSkeletalMeshObjectGPUSkin::ProcessUpdatedDynamicData() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\engine\private\skeletalrendergpuskin.cpp:454]
UE4Editor_Engine!FSkeletalMeshObjectGPUSkin::UpdateDynamicData_RenderThread() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\engine\private\skeletalrendergpuskin.cpp:300]
UE4Editor_Engine!`FSkeletalMeshObjectGPUSkin::Update'::`2'::EURCMacro_SkelMeshObjectUpdateDataCommand::DoTask() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\engine\private\skeletalrendergpuskin.cpp:224]
UE4Editor_Engine!TGraphTask<`FSkeletalMeshObjectGPUSkin::Update'::`2'::EURCMacro_SkelMeshObjectUpdateDataCommand>::ExecuteTask() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\core\public\async\taskgraphinterfaces.h:999]
UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\core\private\async\taskgraph.cpp:932]
UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\core\private\async\taskgraph.cpp:679]
UE4Editor_RenderCore!RenderingThreadMain() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\rendercore\private\renderingthread.cpp:319]
UE4Editor_RenderCore!FRenderingThread::Run() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\rendercore\private\renderingthread.cpp:440]
UE4Editor_Core!FRunnableThreadWin::Run() [d:\build\++ue4+release-4.12+compile\sync\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:74]

Apex Clothing - Crash when adding clothing to mesh after importing the apx file