Fixing possible double cancelling issue

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

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

@@ -50,6 +50,7 @@ public abstract class Countdown {
     }
 
     public void disable() {
+        if(!task.isCancelled())
             task.cancel();
     }