trying to use beautify fill right after calculating scanfill
it segfaults though, a bit clueless on where to go
BM_edge_exists() neesd to be called after all the new faces are created

(otherwise sf->edge->v1->tmp.p will not be connected to
sf->edge->v2->tmp.p yet)

This is still not working. BM_edge_exists is not NULL, but edge->l is,
which is breaking inside BM_mesh_beautify_fill.

(also, only send the non-boundary edges to the beautify routine)
f->len == 3 at that time, we need to store it from early on
(still crashes, but on BLI_gset_haskey)