Fixed a potential null pointer in the task list refresh receiver:

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

@@ -734,7 +734,9 @@ public class TaskListFragment extends ListFragment implements OnScrollListener,
                     || !AstridApiConstants.BROADCAST_EVENT_REFRESH.equals(intent.getAction()))
                 return;
 
-            getActivity().runOnUiThread(new Runnable() {
+            Activity activity = getActivity();
+            if (activity != null) {
+                activity.runOnUiThread(new Runnable() {
                     @Override
                     public void run() {
                         refresh();
@@ -742,6 +744,7 @@ public class TaskListFragment extends ListFragment implements OnScrollListener,
                 });
             }
         }
+    }
 
     /**
      * Called by the RefreshReceiver when the task list receives a refresh