The issue was that the particle spawner mesh had no polygons/faces, resulting in
a NullPointerException in `mfaces`. So check for such cases where the mesh has no polygons,
and if present silently hides that the CD_MFACE layer is not being generated from CD_MPOLY as it should beMeshes spawning particles from faces with with UV's/Vertex-colors but no faces would crash de-referencing a NULL pointer.
Resolve by adding a check for this case and an assertion if CD_MFACE is NULL when the mesh has polygons.