Skip SCALAR assembly in absence of SCALAR vars
Skip SCALAR assembly in absence of SCALAR vars

in FEMSystem::assembly. This is only a slight optimization,
but this enables more asserts/better code for the support
of multiple dimension meshes.

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