window: add safety check

src/gcal-window.c

@@ -405,7 +405,8 @@ update_view (GcalWindow *window)
   priv = gcal_window_get_instance_private (window);
 
   widget = priv->views[priv->active_view];
-
+  if (widget != NULL)
+    {
       header = gcal_view_get_left_header (GCAL_VIEW (widget));
       g_object_set (priv->nav_bar, "left-header", header, NULL);
       g_free (header);
@@ -414,6 +415,7 @@ update_view (GcalWindow *window)
       g_object_set (priv->nav_bar, "right-header", header, NULL);
       g_free (header);
     }
+}
 
 /**
  * view_changed: