Importing a t3d filetype will cause a crash

!!! Changes between version 4.12 and 4.13 for importing these !!!

4.12
There is a crash when importing any t3d (legacy) file through File > Import Into Level using the t3d file option.

4.13
The option to import the file type t3d does not exist in File > Import into Level anylonger, however you can set it to AnyFiles and select the t3d file, which will result in a crash.

Also in 4.13 the option to export as filetype t3d still exists. It looks like there have been some changes to this process, especially with the full scene importer now.

1. Open UE4
2. (OPTIONAL) Export the default scene as a T3D file with File > Export All/Selected
3. Import the .t3d file (File > Import into Level > Select t3d

Regression: Yes

Results: The editor will crash on import

Expected: The t3d should import without crash.

Assertion failed: ActorIndex == 0 [Link Removed] [Line: 526]

KERNELBASE.dll
UE4Editor-Core.dll!FOutputDeviceWindowsError::Serialize() [d:\builds\ue4_main\engine\source\runtime\core\private\windows\windowsplatformoutputdevices.cpp:103]
UE4Editor-Core.dll!FOutputDevice::Logf__VA() [d:\builds\ue4_main\engine\source\runtime\core\private\misc\outputdevice.cpp:86]
UE4Editor-Core.dll!FDebug::AssertFailed() [d:\builds\ue4_main\engine\source\runtime\core\private\misc\outputdevice.cpp:405]
UE4Editor-UnrealEd.dll!ULevelFactory::FactoryCreateText() [d:\builds\ue4_main\engine\source\editor\unrealed\private\factories\editorfactories.cpp:529]
UE4Editor-UnrealEd.dll!UFactory::FactoryCreateFile() [d:\builds\ue4_main\engine\source\editor\unrealed\private\factories\factory.cpp:56]
UE4Editor-UnrealEd.dll!UFactory::ImportObject() [d:\builds\ue4_main\engine\source\editor\unrealed\private\factories\factory.cpp:143]
UE4Editor-UnrealEd.dll!UFactory::StaticImportObject() [d:\builds\ue4_main\engine\source\editor\unrealed\private\factories\factory.cpp:382]
UE4Editor-UnrealEd.dll!UFactory::StaticImportObject() [d:\builds\ue4_main\engine\source\editor\unrealed\private\factories\factory.cpp:315]
UE4Editor-UnrealEd.dll!UEditorEngine::Map_Import() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorserver.cpp:2645]
UE4Editor-UnrealEd.dll!UEditorEngine::HandleMapCommand() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorserver.cpp:5988]
UE4Editor-UnrealEd.dll!UEditorEngine::Exec() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorserver.cpp:5478]
UE4Editor-UnrealEd.dll!UUnrealEdEngine::Exec() [d:\builds\ue4_main\engine\source\editor\unrealed\private\unrealedsrv.cpp:744]
UE4Editor-UnrealEd.dll!FEditorFileUtils::Import() [d:\builds\ue4_main\engine\source\editor\unrealed\private\filehelpers.cpp:1045]
UE4Editor-UnrealEd.dll!FEditorFileUtils::Import() [d:\builds\ue4_main\engine\source\editor\unrealed\private\filehelpers.cpp:1002]
UE4Editor-LevelEditor.dll!TBaseStaticDelegateInstance<void __cdecl(void)>::ExecuteIfSafe() [d:\builds\ue4_main\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:1017]
UE4Editor-Slate.dll!FUICommandList::ExecuteAction() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\commands\uicommandlist.cpp:87]
UE4Editor-Slate.dll!SMenuEntryBlock::OnClicked() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\multibox\smenuentryblock.cpp:1027]
UE4Editor-Slate.dll!SMenuEntryBlock::OnMenuItemButtonClicked() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\multibox\smenuentryblock.cpp:987]
UE4Editor-Slate.dll!TMemberFunctionCaller<SMenuEntryBlock,FReply (__cdecl SMenuEntryBlock::*)(void) __ptr64>::operator()<>() [d:\builds\ue4_main\engine\source\runtime\core\public\delegates\delegateinstanceinterface.h:161]
UE4Editor-Slate.dll!TTupleImpl<TIntegerSequence<unsigned int> >::ApplyAfter<TMemberFunctionCaller<SMenuEntryBlock,FReply (__cdecl SMenuEntryBlock::*)(void) __ptr64> >() [d:\builds\ue4_main\engine\source\runtime\core\public\delegates\tuple.h:115]
UE4Editor-Slate.dll!TBaseSPMethodDelegateInstance<0,SMenuEntryBlock,0,FReply __cdecl(void)>::Execute() [d:\builds\ue4_main\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:317]
UE4Editor-Slate.dll!TBaseDelegate<FReply>::Execute() [d:\builds\ue4_main\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:521]
UE4Editor-Slate.dll!SButton::OnMouseButtonUp() [d:\builds\ue4_main\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:275]
UE4Editor-Slate.dll!SMenuEntryButton::OnMouseButtonUp() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\multibox\smenuentryblock.cpp:385]
UE4Editor-Slate.dll!<lambda_8d0e9a1da76abd0a756a3a9d775f5ed1>::operator()() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4611]
UE4Editor-Slate.dll!FEventRouter::Route<FReply,FEventRouter::FToLeafmostPolicy,FPointerEvent,<lambda_8d0e9a1da76abd0a756a3a9d775f5ed1> >() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:215]
UE4Editor-Slate.dll!FSlateApplication::RoutePointerUpEvent() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4600]
UE4Editor-Slate.dll!FSlateApplication::ProcessMouseButtonUpEvent() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5054]
UE4Editor-Slate.dll!FSlateApplication::OnMouseUp() [d:\builds\ue4_main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5034]
UE4Editor-Core.dll!FWindowsApplication::ProcessDeferredMessage() [d:\builds\ue4_main\engine\source\runtime\core\private\windows\windowsapplication.cpp:1509]
UE4Editor-Core.dll!FWindowsApplication::DeferMessage() [d:\builds\ue4_main\engine\source\runtime\core\private\windows\windowsapplication.cpp:1849]
UE4Editor-Core.dll!FWindowsApplication::ProcessMessage() [d:\builds\ue4_main\engine\source\runtime\core\private\windows\windowsapplication.cpp:744]
UE4Editor-Core.dll!FWindowsApplication::AppWndProc() [d:\builds\ue4_main\engine\source\runtime\core\private\windows\windowsapplication.cpp:666]
USER32.dll
USER32.dll
UE4Editor-Core.dll!FWindowsPlatformMisc::PumpMessages() [d:\builds\ue4_main\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:905]
UE4Editor.exe!FEngineLoop::Tick() [d:\builds\ue4_main\engine\source\runtime\launch\private\launchengineloop.cpp:2759]
UE4Editor.exe!GuardedMain() [d:\builds\ue4_main\engine\source\runtime\launch\private\launch.cpp:156]
UE4Editor.exe!GuardedMainWrapper() [d:\builds\ue4_main\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor.exe!WinMain() [d:\builds\ue4_main\engine\source\runtime\launch\private\windows\launchwindows.cpp:202]
UE4Editor.exe!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264]
kernel32.dll
ntdll.dll
ntdll.dll