Fixing possible double cancelling issue

Signed-off-by: Lixfel <agga-games@gmx.de>

FightSystem_Main/src/de/steamwar/fightsystem/countdown/Countdown.java

@@ -50,7 +50,8 @@ public abstract class Countdown {
     }
 
     public void disable() {
-        task.cancel();
+        if(!task.isCancelled())
+            task.cancel();
     }
 
     private void broadcast(String message){