Actually fix bug causing crashes on live server

The following sequence of events was causing a crash:

1) User sends in decision to server (with the wrong rqid specified).
2) Server receives decision and sends message M to simulator process.
3) User leaves battle and sends the server a message to inform of this.
4) Server removes the user from his or her battle in the main process,
   which sets the user's entry in simulator.player to null.
5) The simulator process processes message M and, since the rqid in
   the decision is wrong, send a resendrequest message back to the
   main process.
6) The main process in resendRequest() tries to access properties of
   the player, which are now null as of event (4), causing a crash.

This commit fixes the problem by making sure that user is not null
before accessing its properties.