clutter/actor: Cancel delayed timelines on removal

Delayed clutter timelines might be removed while they are still in the
process of being executed, but if they are not playing yet their delay
timeout won't be stopped, causing them to be executed anyway, leading to a
potential crash.

In fact if something else keeps a reference on the timelines (i.e. gjs), the
dispose vfunc delay cancellation won't take effect, causing the timelines to
be started and added to the master clock.

To avoid this, expose clutter_timeline_cancel_delay() function and call it
if a timeline is not playing but has a delay set.

Fixes https://gitlab.gnome.org/GNOME/mutter/issues/815
https://gitlab.gnome.org/GNOME/mutter/merge_requests/805

clutter/clutter/clutter-actor.c

@@ -19484,6 +19484,8 @@ transition_closure_free (gpointer data)
 
       if (clutter_timeline_is_playing (timeline))
         clutter_timeline_stop (timeline);
+      else if (clutter_timeline_get_delay (timeline) > 0)
+        clutter_timeline_cancel_delay (timeline);
 
       /* remove the reference added in add_transition_internal() */
       g_object_unref (clos->transition);

clutter/clutter/clutter-private.h

@@ -315,6 +315,8 @@ gboolean        _clutter_run_progress_function  (GType gtype,
                                                  gdouble progress,
                                                  GValue *retval);
 
+void            clutter_timeline_cancel_delay (ClutterTimeline *timeline);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_PRIVATE_H__ */

clutter/clutter/clutter-timeline.c

@@ -424,7 +424,7 @@ clutter_timeline_set_custom_property (ClutterScriptable *scriptable,
     g_object_set_property (G_OBJECT (scriptable), name, value);
 }
 
-static void
+void
 clutter_timeline_cancel_delay (ClutterTimeline *timeline)
 {
   g_clear_handle_id (&timeline->priv->delay_id, g_source_remove);