Leaving game crashes the server

[xird]

I haven't tried this again, but this it what happened:

• Two player game in progress
• My secondary browser, Firefox, timed out and the monster got killed as it should
• My primary browser, Chrome, showed that I'd won
• I clicked "leave game"
• Server crashed

ROKServerGame.js:1522: * FIXME: Clicking Leave Game after opponent disconnected crashed the server.

[S-Bartfast]

In particular it appears the the crashed is caused on what is currently line 99 of ROKServerLobby.js which reads:
target_socket.emit("update_lobby", send_object);
target_socket is "undefined".

[xird]

I've added more checks to make sure the socket exists before trying to emit to it.