Crash while using the Delete Button in the HLOD Outliner while a Generated Proxy Mesh is opened in the Static Mesh Editor

When deleting a generated proxy mesh from the HLOD Outliner using the Delete Button while the generated proxy mesh is opened in the static mesh editor will cause the editor to crash.

Workaround: Use right-click on the clusters to delete or close the static mesh editor that has that particular generated proxy mesh before clicking the delete button.

1. Enable HLODs for your Level.
2. Open the HLOD Outliner window
3. Add some meshes to the scene to be clustered
4. Click Generate Clusters (default settings works)
5. Click Generate Proxy Meshes
6. Open the generated proxy mesh and leave it open with the static mesh editor
7. Click the button for "Delete Clusters"

Regression: No

Results: Editor will crash
Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0xffffffff

LoginId:7d8a1a304be9658328c158a3d14cc774
EpicAccountId:7c6293d6bf1940c0bc89e1494c5ba9d7

Access violation - code c0000005 (first/second chance not available)

UE4Editor_StaticMeshEditor!FStaticMeshEditorViewportClient::Draw() [d:\builds\ue4_main\engine\source\editor\staticmesheditor\private\staticmesheditorviewportclient.cpp:444]
UE4Editor_Renderer!FSceneRenderer::FSceneRenderer() [d:\builds\ue4_main\engine\source\runtime\renderer\private\scenerendering.cpp:1153]
UE4Editor_Renderer!FDeferredShadingSceneRenderer::FDeferredShadingSceneRenderer() [d:\builds\ue4_main\engine\source\runtime\renderer\private\deferredshadingrenderer.cpp:194]
UE4Editor_Renderer!FRendererModule::BeginRenderingViewFamily() [d:\builds\ue4_main\engine\source\runtime\renderer\private\scenerendering.cpp:1868]
UE4Editor_UnrealEd!FEditorViewportClient::Draw() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorviewportclient.cpp:3379]
UE4Editor_Engine!FViewport::Draw() [d:\builds\ue4_main\engine\source\runtime\engine\private\unrealclient.cpp:1185]
UE4Editor_UnrealEd!UEditorEngine::UpdateSingleViewportClient() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorengine.cpp:2007]
UE4Editor_UnrealEd!UEditorEngine::Tick() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorengine.cpp:1783]
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [d:\builds\ue4_main\engine\source\editor\unrealed\private\unrealedengine.cpp:391]
UE4Editor!FEngineLoop::Tick() [d:\builds\ue4_main\engine\source\runtime\launch\private\launchengineloop.cpp:3019]
UE4Editor!GuardedMain() [d:\builds\ue4_main\engine\source\runtime\launch\private\launch.cpp:166]
UE4Editor!GuardedMainWrapper() [d:\builds\ue4_main\engine\source\runtime\launch\private\windows\launchwindows.cpp:130]
UE4Editor!WinMain() [d:\builds\ue4_main\engine\source\runtime\launch\private\windows\launchwindows.cpp:206]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253]
kernel32
ntdll