Fixed a potential null pointer exception in calendar event creation

astrid/plugin-src/com/todoroo/astrid/gcal/GCalHelper.java

@@ -40,6 +40,7 @@ public class GCalHelper {
         if (gcalCreateEventEnabled) {
             ContentResolver cr = ContextManager.getContext().getContentResolver();
             Uri calendarUri = GCalHelper.createTaskEvent(t, cr, new ContentValues());
+            if (calendarUri != null)
                 t.setValue(Task.CALENDAR_URI, calendarUri.toString());
         }
     }