Don't error on n_local_dofs==0 corner case
Don't error on n_local_dofs==0 corner case

This fixes the
userobjects/shape_element_user_object.shape_element_user_object test
for me on 13+ processors (and hopefully for Civet too - it was the
nightly tests from #9430 that caught the overzealous error.

nuclear-wizard/moose,andrsd/moose,milljm/moose,permcody/moose,milljm/moose,permcody/moose,Chuban/moose,yipenggao/moose,andrsd/moose,bwspenc/moose,friedmud/moose,Chuban/moose,harterj/moose,yipenggao/moose,SudiptaBiswas/moose,lindsayad/moose,andrsd/moose,dschwen/moose,harterj/moose,andrsd/moose,idaholab/moose,permcody/moose,SudiptaBiswas/moose,laagesen/moose,jessecarterMOOSE/moose,dschwen/moose,andrsd/moose,dschwen/moose,dschwen/moose,SudiptaBiswas/moose,friedmud/moose,milljm/moose,lindsayad/moose,jessecarterMOOSE/moose,sapitts/moose,laagesen/moose,SudiptaBiswas/moose,idaholab/moose,harterj/moose,sapitts/moose,dschwen/moose,SudiptaBiswas/moose,Chuban/moose,milljm/moose,sapitts/moose,YaqiWang/moose,YaqiWang/moose,harterj/moose,bwspenc/moose,bwspenc/moose,jessecarterMOOSE/moose,idaholab/moose,nuclear-wizard/moose,idaholab/moose,YaqiWang/moose,laagesen/moose,lindsayad/moose,yipenggao/moose,lindsayad/moose,sapitts/moose,nuclear-wizard/moose,laagesen/moose,milljm/moose,friedmud/moose,Chuban/moose,sapitts/moose,permcody/moose,bwspenc/moose,yipenggao/moose,bwspenc/moose,harterj/moose,idaholab/moose,YaqiWang/moose,lindsayad/moose,nuclear-wizard/moose,jessecarterMOOSE/moose,laagesen/moose,jessecarterMOOSE/moose,friedmud/moose