Fix bad shared_ptr dereference.

Always verify that map entries exist before accessing the shared
pointer held by the map.

smtk/bridge/polygon/operators/CreateFaces.cxx

@@ -662,12 +662,15 @@ struct Neighborhood
       winner = this->m_regionIds.mergeSets(idA, idB);
       RegionIdSet::value_type loser = (winner == idA ? idB : idA);
       // If this is a new region, create a record for it.
-      if (!this->m_regions[winner])
+      if (this->m_regions.find(winner) == this->m_regions.end())
         {
         this->m_regions[winner] = smtk::make_shared<Region>(*ringB, !isOutB);
         }
-      this->m_regions[winner]->merge(this->m_regions[loser].get());
-      this->m_regions.erase(loser);
+      if (this->m_regions.find(loser) != this->m_regions.end())
+        {
+        this->m_regions[winner]->merge(this->m_regions[loser].get());
+        this->m_regions.erase(loser);
+        }
       }
     else
       { // Add coedges (of exiting edges on inside of A--B) to region.