Blender Git Loki

Fix T50851: Array modifier generating invalid geometry.

We had handling of fully duplicated polygons already, but... absolutely
nothing to sanitize partially merged polygons! This were giving us
totally invalid geometry, with duplicated vertices in single poly,
invalid edges, etc.

Now we do check for invalid loops inside polys, and generate new edges
as needed to get only valid polys.

For some reason this was a nightmare to get running fully OK, playing
with old and new indices is really, really mind breaking.