Setting a console variable interacts with window state

When the game window is set to be windowed and maximized, setting a console variable changes the window's state from being maximized to its default size. 

This is a regression as it is working as expected in 4.19.2 (CL-4033788). This issue was reported and tested in 4.20.1 (CL-4233996). It was reproduced in Main 4.21 (CL-4280116). 

1. Open the UE4 Editor and create a blank project
2. Click the dropdown arrow beside Play and select "Play in Standalone Game"
3. Maximize the game window
4. Set a console variable value through the console, for example 'r.PostProcessAAQuality 0'

Results: The game window reverts to its default size

Expected: The game window remains maximized