d52551401e
`ARegion.alignment` unfortunately is a mixture of value and bitflag enumerations. When checking for left/right/top/bottom region alignment, the flags have to be masked out usually. Most of the fixed cases here probably didn't cause issues in practice, but could in fact break at any point when surrounding logic changes. In fact the assert in #region_visible_rect_calc() failed in an older file from https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949035. This fixes it.