When selecting the pick regions for an actor we were not considering
whether the actor was allocated and that was causing issues where the
preferred width/height of the actor was used when deciding whether
the actor should be considered as a pick target.
Check if the actor has a valid allocation, in addition to being mapped
and being in pick mode, in clutter_actor_should_pick_paint().
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1169
(cherry picked from commit 902302a174483eabe796227a3fc82a36770f40b2)
82f3bdd14e