Blender Git Loki

Fix for [#28528] Disappearing Faces

Bring back some old scanfill code to handle tesselating polys with some zero-length edges. This code used to cause #4544 but I haven't been able to recreate that now, so I'm going to revive the old code and if #4544 does come back, we'll have to fix it some other way I guess (or come up with a better solution for zero-length edges in polys).