clutter/actor-destroy: Check that destroying the actor clears the children
Commit df7d8e2c highlights a crash on test_destroy_destroy, in fact it could happen that calling clutter_actor_destroy on a child while iterating on the list, would implicitly call test_destroy_remove that tries to modify the list at the same time. Causing a memory error.
So instead of manually free the children list, just ensure that this list is valid and that when the object destruction is done, this is free'd.
See: !576 (merged)
This happens 100% of the times when using
G_SLICE=always-malloc (and probably
MALLOC_CHECK_ != 0.