Store WorkItemID by a local variable

[WJsjtu]

https://github.com/sideeffects/HoudiniEngineForUnreal/blob/24a7e9ee059800826b1dcec41b369494f231db72/Source/HoudiniEngine/Private/HoudiniPDGManager.cpp#L1649-L1660

WorkItemID should be stored as a local variable before line 1656, since reading a value of referenced structure that has already been destructed (line 1657) can be dangerous. When debugging editor or game with strict address case (e.g. enable unreal build with ASan), it always crashes.