Fixed a possible null pointer exception in showListsHelp()

astrid/src/com/todoroo/astrid/activity/TaskListFragment.java

@@ -894,12 +894,14 @@ public class TaskListFragment extends ListFragment implements OnScrollListener,
             return;
         if (!Preferences.getBoolean(
                 R.string.p_showed_lists_help, false)) {
-            if (AndroidUtilities.isTabletSized(getActivity())) {
-                ((AstridActivity) getActivity()).getFilterListFragment().showAddListPopover();
+            AstridActivity activity = (AstridActivity) getActivity();
+            if (activity != null) {
+                if (AndroidUtilities.isTabletSized(activity)) {
+                    activity.getFilterListFragment().showAddListPopover();
                 } else {
-                ActionBar ab = ((AstridActivity) getActivity()).getSupportActionBar();
+                    ActionBar ab = activity.getSupportActionBar();
                     View anchor = ab.getCustomView().findViewById(R.id.lists_nav);
-                HelpInfoPopover.showPopover(getActivity(),
+                    HelpInfoPopover.showPopover(activity,
                             anchor, R.string.help_popover_switch_lists, null);
                 }
                 Preferences.setBoolean(
@@ -907,6 +909,7 @@ public class TaskListFragment extends ListFragment implements OnScrollListener,
                         true);
             }
         }
+    }
 
     /*
      * ======================================================================