[NL] MCM: getSubset checks for valid global idx.

If the boundary mesh is larger then the definition region
of the bulk component, then a nop is returned.
This usually indicates wrong geometry or something horrible.

NumLib/DOF/MeshComponentMap.cpp

@@ -171,8 +171,10 @@ MeshComponentMap MeshComponentMap::getSubset(
 
         for (auto component_id : component_ids)
         {
-            subset_dict.insert({new_location, component_id,
-                                getGlobalIndex(bulk_location, component_id)});
+            auto const global_index =
+                getGlobalIndex(bulk_location, component_id);
+            assert (global_index != nop);
+            subset_dict.insert({new_location, component_id, global_index});
         }
     }