Paolo Borelli authored Feb 16, 2014 and Matthias Clasen committed Jun 21, 2015

When the stack is destroyed we do not want to waste time running
animations and notifying listeners about which is our current
visible child.

This is not only an optimization, but it is important for the stack
switcher widgets: since they are in another branch of the hieratchy
we do not want to get notifications while the stack is being destroyed.

Based on a patch by Paolo Borelli
https://bugzilla.gnome.org/show_bug.cgi?id=724506