Crash when using ListStreamingTextures with VirtualTexturePrefetchMips

The ListStreamingTextures command causes a crash in FRenderAssetStreamingManager::HandleListStreamingRenderAssetsCommand when there is a virtual texture that uses crashes when encountering one of these textures.

It seems like the issue is that for VTs with VirtualTexturePrefetchMips, TextureMips is empty, so the OutputMipsString lambda needs to look in (*TexturePlatformData)->VTData instead to get the size of OutputIndex

1. Add a 512x512 texture and convert it to a streaming virtual texture
2. Set VirtualTexturePrefetchMips to 8
3. Use the texture in a Material and assign the Material to a mesh in the scene
4. Run the ListStreamingTextures console command.

Expected

The textures are listed

Actual

A crash occurs

> [Inline Frame] UnrealEditor-Engine.dll!TArray>::RangeCheck(int) Line 1095 C++
[Inline Frame] UnrealEditor-Engine.dll!TArray>::operator[](int) Line 1173 C++
[Inline Frame] UnrealEditor-Engine.dll!TArray>::operator[](int) Line 1186 C++
[Inline Frame] UnrealEditor-Engine.dll!TIndirectArray>::operator[](int) Line 150 C++
UnrealEditor-Engine.dll!FRenderAssetStreamingManager::HandleListStreamingRenderAssetsCommand::__l50::::operator()(int OutputIndex) Line 2408 C++
UnrealEditor-Engine.dll!FRenderAssetStreamingManager::HandleListStreamingRenderAssetsCommand(const wchar_t * Cmd, FOutputDevice & Ar) Line 2436 C++
UnrealEditor-Engine.dll!FRenderAssetStreamingManager::Exec(UWorld * InWorld, const wchar_t * Cmd, FOutputDevice & Ar) Line 3131 C++
UnrealEditor-Engine.dll!FStreamingManagerCollection::Exec(UWorld * InWorld, const wchar_t * Cmd, FOutputDevice & Ar) Line 1125 C++
UnrealEditor-Engine.dll!UEngine::Exec(UWorld * InWorld, const wchar_t * Cmd, FOutputDevice & Ar) Line 5443 C++
UnrealEditor-UnrealEd.dll!UUnrealEdEngine::Exec(UWorld * InWorld, const wchar_t * Stream, FOutputDevice & Ar) Line 662 C++
UnrealEditor-UnrealEd.dll!FConsoleCommandExecutor::ExecInternal(const wchar_t * Input) Line 146 C++
UnrealEditor-UnrealEd.dll!FConsoleCommandExecutor::Exec(const wchar_t * Input) Line 81 C++