Fix overzealous assert
Fix overzealous assert

Our assertion wasn't compatible with our workaround for a METIS bug;
this gets exposed when partitioning a completely disconnected mesh.

Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh