Fix true_centroid() with --disable-amr
Fix true_centroid() with --disable-amr

libMesh/libmesh,jwpeterson/libmesh,libMesh/libmesh,dschwen/libmesh,dschwen/libmesh,dschwen/libmesh,libMesh/libmesh,libMesh/libmesh,jwpeterson/libmesh,dschwen/libmesh,libMesh/libmesh,dschwen/libmesh,libMesh/libmesh,jwpeterson/libmesh,dschwen/libmesh,libMesh/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,libMesh/libmesh,dschwen/libmesh,dschwen/libmesh,jwpeterson/libmesh,jwpeterson/libmesh