fixed NPE on navDrawerData

app/src/main/java/de/danoeh/antennapod/activity/MainActivity.java

@@ -365,12 +365,14 @@ public class MainActivity extends ActionBarActivity implements NavDrawerActivity
             return -1;
         } else { // last fragment was not a list, but a feed
             long feedId = Long.parseLong(lastFragment);
+            if (navDrawerData != null) {
                 List<Feed> feeds = navDrawerData.feeds;
                 for (int i = 0; i < feeds.size(); i++) {
                     if (feeds.get(i).getId() == feedId) {
                         return i + navAdapter.getSubscriptionOffset();
                     }
                 }
+            }
             return -1;
         }
     }