Use elem->dim() in build_*_solution_vector
Use elem->dim() in build_*_solution_vector

This fixes mixed-dimension output for me.

libMesh/libmesh,jwpeterson/libmesh,dschwen/libmesh,BalticPinguin/libmesh,libMesh/libmesh,roystgnr/libmesh,dschwen/libmesh,libMesh/libmesh,dschwen/libmesh,roystgnr/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,BalticPinguin/libmesh,libMesh/libmesh,capitalaslash/libmesh,dschwen/libmesh,BalticPinguin/libmesh,dschwen/libmesh,jwpeterson/libmesh,libMesh/libmesh,dschwen/libmesh,libMesh/libmesh,libMesh/libmesh,libMesh/libmesh,jwpeterson/libmesh,dschwen/libmesh,jwpeterson/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,roystgnr/libmesh,roystgnr/libmesh,capitalaslash/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,dschwen/libmesh,jwpeterson/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,jwpeterson/libmesh