DX12 crash by lost device while building PSO

It seems to be occurred when exiting fullscreen exclusive mode during the PSO build.
And it seems to happen during the loading screen as well as the PSO build.

What I suspect is that when focus loss has occurred, the loading screen tick continues on the render thread until the engine handles device lost.

For example, UpdateFullscreenState() and ResizeViewport() in FSceneViewport::ResizeFrame() would have to be handled earlier, but it crashed before then that.

In other words, render thread suspended in FSceneViewport::UpdateViewportRHI(), but it crashed by executing RHI commands in the render thread before it is suspended.

1. create shootergame project with UE 4.25.3
2. overwrite attached ini files to Config folder
3. package windows x64 build
4. run shootergame with commandline arguments "-dx12 -log -messaging"
5. repeat alt+tab during gameplay for PSO build