New game started from outside of lobby has been handled

src/main/java/ch/unibas/dmi/dbis/cs108/multiplayer/server/ClientHandler.java

@@ -311,6 +311,8 @@ public class ClientHandler implements Runnable {
       t.start();
     } catch (TrainOverflow e) {
       LOGGER.warn(e.getMessage());
+    } catch (NullPointerException e) {
+      LOGGER.warn("Client is not in a lobby");
     }
   }