Blender Git Loki

Fix T52640: crash when opening image file browser in some cases.

There was some invalid state in the screen here, some areas had
sa->full set even though no screen was maximized, which then caused
a restore from the wrong (empty) area, which then led to spacedata
being empty and a crash.

This fix properly clears the sa->full after restore, and also fixes
existing .blend files in such an invalid state.