Issue was caused by performing conversion from FTFaces to materials from
the end of lib_link_mesh, where tesselated faces were cleared already.
This conversion can't be switched to BMesh structures because in future
MTexPolys could be changed in a way, that versioning stuff wouldn't work
any more. Another issue is that making such a conversion per-mesh would
lead to quite a code spagetti, which is difficult to follow.
Solved by splitting per-mesh cycle in lib_link_mesh, so now it consists
of three steps:
- Do linking stuff such as custom data layers, materials. Perform a
Conversion stuff like tessface -> polys.
- Convert all MTFaces to materials. This conversion handles all meshes
and creates needed materials.
- Free tessfaces, mark mesh as linked.
Such a separation shouldn't noticeably affect on speed of linking.
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