Blender Git Loki

Fix T91889 Exact boolean sometimes drops triangles.

The problem is that the fast triangulator (based on polyfill)
sometimes makes degenerate triangles. Commit 8115f0c5bd91f had
a check for degenerate triangles but it wasn't thorough enough.
This commit uses a more thorough (and pessimistic) test for
degenerate triangles, using the exact triangulator in those cases.