Description

Importing an Alembic File with "Skip Empty Frames at the Start of Alembic Sequence" Enabled Causes Crash.

Found in 4.20 Preview 5 CL# 4173640 and 4.21 CL# 4207835

Steps to Reproduce
  1. Open the editor
  2. Import the file below as "Geometry Cache" 
  3. Enable "Skip Empty Frames at Start of Alembic Sequence"
  4. Click Import

Results:
The engine will crash

Expected:
The alembic file would be imported

[Link Removed]

Callstack
Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\Main\Engine\Source\Runtime\Core\Public\Containers/Array.h] [Line: 611] Array index out of bounds: 2258 from an array of size 2256

UE4Editor_Core!FDebug::AssertFailed() [d:\main\engine\source\runtime\core\private\misc\assertionmacros.cpp:425]
UE4Editor_AlembicLibrary!AbcImporterUtilities::GenerateSmoothingGroupsIndices() [d:\main\engine\plugins\experimental\alembicimporter\source\alembiclibrary\private\abcimportutilities.cpp:737]
UE4Editor_AlembicLibrary!FAbcPolyMesh::SetFrameAndTime() [d:\main\engine\plugins\experimental\alembicimporter\source\alembiclibrary\private\abcpolymesh.cpp:165]
UE4Editor_AlembicLibrary!FAbcFile::ReadFrame() [d:\main\engine\plugins\experimental\alembicimporter\source\alembiclibrary\private\abcfile.cpp:355]
UE4Editor_AlembicLibrary!<lambda_a39ac5b1e2ade9df8718ce618b286a9d>::operator()() [d:\main\engine\plugins\experimental\alembicimporter\source\alembiclibrary\private\abcfile.cpp:398]
UE4Editor_AlembicLibrary!FParallelForData::Process() [d:\main\engine\source\runtime\core\public\async\parallelfor.h:134]
UE4Editor_AlembicLibrary!TGraphTask<FParallelForTask>::ExecuteTask() [d:\main\engine\source\runtime\core\public\async\taskgraphinterfaces.h:829]
UE4Editor_Core!FTaskThreadAnyThread::ProcessTasks() [d:\main\engine\source\runtime\core\private\async\taskgraph.cpp:936]
UE4Editor_Core!FTaskThreadAnyThread::ProcessTasksUntilQuit() [d:\main\engine\source\runtime\core\private\async\taskgraph.cpp:801]
UE4Editor_Core!FTaskThreadBase::Run() [d:\main\engine\source\runtime\core\private\async\taskgraph.cpp:516]
UE4Editor_Core!FRunnableThreadWin::Run() [d:\main\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:76]

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Fixed
ComponentOLD - Anim
Affects Versions4.204.21
Target Fix4.21
Fix Commit4495074
Main Commit4551290
Release Commit4495074
CreatedJul 13, 2018
ResolvedOct 22, 2018
UpdatedNov 8, 2018
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