[core] more checks on face validity, prevent openmesh assert.
[core] more checks on face validity, prevent openmesh assert.

Remove duplicated vertices index in face list, this is not handled by
OpenMesh [on purpose](https://graphics.rwth-aachen.de:9000/OpenMesh/OpenMesh/-/issues/66)

Zouch/Radium-Engine,Zouch/Radium-Engine