gui: #5339 Disable GEGL Op menu action if no image is open

Because "GEGL Operations..." menu action should be active only
if image is open

app/actions/tools-actions.c

@@ -797,4 +797,12 @@ void
 tools_actions_update (GimpActionGroup *group,
                       gpointer         data)
 {
+  GimpImage *image = action_data_get_image (data);
+
+#define SET_SENSITIVE(action,condition) \
+        gimp_action_group_set_action_sensitive (group, action, (condition) != 0)
+
+  SET_SENSITIVE ("tools-gegl", image);
+
+#undef SET_SENSITIVE
 }