Blender Git Loki

Fix invalid min/max sizes of global areas after loading factory settings

Simply loading factory settings and dragging an area separator
immediately after would cause an assert because of these invalid sizes.

Seems that since rB07499c04f612 we correctly initialize DPI related
UserPref values with 0, which caused DPI dependant initialization of
global areas to set ScrArea.global.size_min/max to 0 too.