fixed hostage cash bug

src/de/tudarmstadt/informatik/hostage/ui2/activity/MainActivity.java

@@ -476,6 +476,8 @@ public class MainActivity extends Activity {
 	@Override
 	public void onBackPressed() {
 		if (getFragmentManager().getBackStackEntryCount() == 1) {
+			MainActivity.getInstance().getHostageService().stopListeners();
+			MainActivity.getInstance().stopAndUnbind();
 			finish();
 		} else {
 			super.onBackPressed();