Check for non-null activity when showing sort options

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

@@ -1215,9 +1215,12 @@ public class TaskListFragment extends ListFragment implements OnScrollListener,
             return true;
         case MENU_SORT_ID:
             StatisticsService.reportEvent(StatisticsConstants.TLA_MENU_SORT);
+            Activity activity = getActivity();
+            if (activity != null) {
                 AlertDialog dialog = SortSelectionActivity.createDialog(
                         getActivity(), hasDraggableOption(), this, sortFlags, sortSort);
                 dialog.show();
+            }
             return true;
         case MENU_SYNC_ID:
             StatisticsService.reportEvent(StatisticsConstants.TLA_MENU_SYNC);