When propagating overhangs to be supported, the regions are newly
properly merged and regularized.
Fix of Stuck at "preparing infill" with "only infill where needed" enabled 1.41.2 #1696
"Only infill where needed" makes slicer crash for some models #6385
[BUG] Slicing stuck for 14h now, 0.8 NZL Ender 5+ Gyroid infill only where need