Prevent crash in RSS screen when moving away.

android/src/org/transdroid/gui/rss/RssListingFragment.java

@@ -501,8 +501,10 @@ public class RssListingFragment extends Fragment implements OnTouchListener, OnS
 
 	private void setProgressBar(boolean b) {
 		inProgress = b;
+		if (getSupportActivity() != null) {
 			getSupportActivity().invalidateOptionsMenu();
 		}
+	}
 
     /*@Override
     public boolean onTouchEvent(MotionEvent me) {