a11y: Hack around infinite loops in parent setting

a11y: Hack around infinite loops in parent setting

This is kind of a hack to get rid of infinite loops that occur when
child accessibles try to set their parent upon creation but the parent
accessible creates its children in the initialize vfunc. Because in that
case, the parent will not have an accessible set when the child tries to
access it, because it is still initializing itself. Which will cause a
new accessible to be created.

https://bugzilla.gnome.org/show_bug.cgi?id=660687