BUG: OBJImporter fails if a texture map occurs more than once.
If an mtl file refers to a texture map file more than once, the generated texture filename consists of the original name dupilcated n times.
For example: newmtl material0 map_Ka abc.png map_Kd abc.png map_Ks abc.png
will try open a fileabc.pngabc.pngabc.png