Stop start-delay-timer instead of auto-start-timer on empty lobby.

Due to the start-delay-timer holding a reference to the
auto-start-timer as its internal callback, the start-delay-timer
should be stopped, when both timers should be stopped.

src/com/garbagemule/MobArena/ArenaImpl.java

@@ -666,7 +666,7 @@ public class ArenaImpl implements Arena
 
             // Last lobby player leaving? Stop the timer
             if (lobbyPlayers.size() == 1) {
-                autoStartTimer.stop();
+                startDelayTimer.stop();
             }
         }