null check in wifidirect eventhandler for onpause

src/de/tudarmstadt/informatik/hostage/sync/wifi_direct/WiFiP2pEventHandler.java

@@ -51,8 +51,11 @@ public class WiFiP2pEventHandler implements WifiP2pManager.ChannelListener {
     }
 
     public void onPause() {
-        activity.unregisterReceiver(receiver);
-        receiver = null;
+        if (receiver == null) {
+            activity.unregisterReceiver(receiver);
+            receiver = null;
+        }
+
     }
 
     @Override