Handle fracturing a destructible mesh when the source mesh has been deleted without a crash.

When attempting to fracture a destructible where the source static mesh has been deleted we get a crash in APEX.

APEX can't seem to find any root leaf nodes to begin fracturing upon. This does not happen when the mesh is present.

To repro, open the project in the UDN ticket and then open any destructible mesh and attempt to fracture it.

We should more gracefully handle this situation (at least without a crash) or attempt to make the import from apex asset work in this case.

1) Open UDN project
2) Open cup destructible mesh
3) Click fracture

APEX_DestructiblePROFILE_x64 APEX_DestructiblePROFILE_x64 UE4Editor_Engine!UDestructibleFractureSettings::CreateVoronoiSitesInRootMesh() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\engine\private\destructiblefracturesettings.cpp:488] UE4Editor_DestructibleMeshEditor!FDestructibleMeshEditorViewportClient::Fracture() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\editor\destructiblemesheditor\private\sdestructiblemesheditorviewport.cpp:218] UE4Editor_DestructibleMeshEditor!TBaseSPMethodDelegateInstance<0,FDestructibleMeshEditorViewportClient,0,TTypeWrapper __cdecl(void)>::Execute() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:282] UE4Editor_DestructibleMeshEditor!TBaseSPMethodDelegateInstance<0,FDestructibleMeshEditorViewportClient,0,void __cdecl(void)>::ExecuteIfSafe() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:388] UE4Editor_Slate!FUICommandList::ExecuteAction() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\framework\commands\uicommandlist.cpp:75] UE4Editor_Slate!SToolBarButtonBlock::OnClicked() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\framework\multibox\stoolbarbuttonblock.cpp:296] UE4Editor_Slate!TMemberFunctionCaller::operator()<>() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\delegates\delegateinstanceinterface_variadics.h:161] UE4Editor_Slate!TTupleImpl >::ApplyAfter_ExplicitReturnType >() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\delegates\tuple.h:113] UE4Editor_Slate!TBaseSPMethodDelegateInstance<0,SToolBarButtonBlock,0,FReply __cdecl(void)>::Execute() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:282] UE4Editor_Slate!TBaseDelegate::Execute() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\delegates\delegatesignatureimpl_variadics.inl:440] UE4Editor_Slate!SButton::OnMouseButtonUp() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:225] UE4Editor_Slate!::operator()() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4170] UE4Editor_Slate!FEventRouter::Route >() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:212] UE4Editor_Slate!FSlateApplication::ProcessMouseButtonUpEvent() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4173] UE4Editor_Slate!FSlateApplication::OnMouseUp() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4133] UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\private\windows\windowsapplication.cpp:1406] UE4Editor_Core!FWindowsApplication::DeferMessage() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\private\windows\windowsapplication.cpp:1711] UE4Editor_Core!FWindowsApplication::ProcessMessage() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\private\windows\windowsapplication.cpp:706] UE4Editor_Core!FWindowsApplication::AppWndProc() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\private\windows\windowsapplication.cpp:628] user32 user32 UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:792] UE4Editor!FEngineLoop::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\launch\private\launchengineloop.cpp:2323] UE4Editor!GuardedMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\launch\private\launch.cpp:142] UE4Editor!GuardedMainWrapper() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\launch\private\windows\launchwindows.cpp:126] UE4Editor!WinMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\launch\private\windows\launchwindows.cpp:200]

error message when install in U.E 5.3 - IS-IN-FCO2-82

I am not able to find world outliner how to enable it?

How can i modify the param name in EQS node

Undefined sysmbol: typeinfo for AActor when cross-compile linux dedicated server on windows

Bonjour j'ai un petit problème c'est que je ne vois plus l'onglet "scability" pour changer les graphismes de uefn et j'ai pas trouvé l'option pour le faire revenir ?

Delay nodes occasionally don't fire the "Completed" output in a nativized build

When I open UE4 4.24.3 it appears that. Does anyone know how to solve?

How to achieve HLSL Multiple Render Target in Material blueprints?

I can't open my map from the editor.

Error UE5 5.0.3