Note that issue has several levels here actually, first one was metaball's materials
not being properly copied into new mesh (code was commented out because of some crash it
seems, made it a bit closer to mesh one and got no crash at all...).
Then, we were calling test_object_materials when ob->data is actually *not* new tmpmesh!
Will remove this call completely in next commit (to make it easier to bisect), I cannot see
any case where object would be assigned with newly generated tmpmesh in this func.
1270ab91be