When an empty project using exclusive fullscreen is alt+tabbed it freezes.

DX9 and DX11, in DX9 I can't even alt+tab properly - getting black screen.

Repro steps:

1. Build the project.

2. Run it.

3. Alt+tab to desktop.

4. Try to get back to the game.

The issue seems to be introduced in 5.4.1p2 and somewhere in 5.3.6pX since it works fine in 5.4.1f1.