Blender Git Loki

Fix stashed full-screens returning to wrong layout

Steps to reproduce were:
* Maximize area (Shift+Spacebar in 2.7, Ctrl+Spacebar in 2.8)
* Open temp file browser (Ctrl+O)
* Cancel file browser (Esc) - should return to previous full-screen
* Press "Return to Previous" button
The previously maximized area would turn into a file-browser.

Note that the issue will still happen when opening old files saved while
in maximized area full-screen.