fix new bug: allow PluginFunctions::getObject() to fail without crashing.

ObjectTypes/HexahedralMesh/PluginFunctionsHexahedralMesh.cc

@@ -108,7 +108,7 @@ bool getObject( int _identifier, HexahedralMeshObject*& _object ) {
   BaseObjectData* object = 0;
   PluginFunctions::getObject(_identifier,object);
 
-  _object = hexahedralMeshObject(object);
+  _object = object ? hexahedralMeshObject(object) : nullptr;
   return ( _object != 0 );
 }
 

ObjectTypes/PolyhedralMesh/PluginFunctionsPolyhedralMesh.cc

@@ -108,7 +108,7 @@ bool getObject( int _identifier, PolyhedralMeshObject*& _object ) {
   BaseObjectData* object = 0;
   PluginFunctions::getObject(_identifier,object);
 
-  _object = polyhedralMeshObject(object);
+  _object = object ? polyhedralMeshObject(object) : nullptr;
   return ( _object != 0 );
 }
 

ObjectTypes/TetrahedralMesh/PluginFunctionsTetrahedralMesh.cc

@@ -102,7 +102,7 @@ bool getObject( int _identifier, TetrahedralMeshObject*& _object ) {
   BaseObjectData* object = 0;
   PluginFunctions::getObject(_identifier,object);
 
-  _object = tetrahedralMeshObject(object);
+  _object = object ? tetrahedralMeshObject(object) : nullptr;
   return ( _object != 0 );
 }