Blender Git Loki

Fix a number of small errors in area coordinate handling

For example collapsing the lower part of the topbar with 2x interface scale
would hide the top-bar header region. There were also more asserts when changing
window size and moving area edges afterwards (same assert as in T55298).
Fixes are similar to e626998a262ebe4f.

With all the recent fixes I've done, area geometry handling should be stable
again. Let's hope I'm right :)