Make hardest room "Dimension VVVVVV" if it has no room name

The only places where you can die in a room without a room name is the
Overworld, and I feel that calling it Dimension VVVVVV is appropriate.

You can't naturally die in The Ship nor the Secret Lab, and you can only
do it by pressing R, so I didn't feel it appropriate to add checks to
make the hardest room be "The Ship" or "The Secret Lab" if you managed
to get your hardest room to be a room in either of those areas.

desktop_version/src/Game.cpp

@@ -4171,6 +4171,10 @@ void Game::gethardestroom( mapclass& map )
             if (roomx == 50 && roomy == 53) hardestroom =map.specialnames[6];
             if (roomx == 50 && roomy == 54) hardestroom = map.specialnames[7];
         }
+        else if (map.roomname == "")
+        {
+            hardestroom = "Dimension VVVVVV";
+        }
     }
 }