If we are transitioning the label from 0 to its natural height, we
must set natural-height-set again after querying the preferred height,
otherwise Clutter would skip the transition.
However when transitioning in the opposite direction, setting the
property to true can go horribly wrong:
If the actor hasn't been allocated before, it will store a fixed
natural height of 0. But as there is no fixed min-height, we can
end up with min-height > natural-height, which is a fatal error.
(This isn't an issue when *actually* setting a fixed height, as
that will set both natural and minimum height)
So instead of always setting natural-height-set to true, restore
its previous value to fix the issue.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/2255
3633e1feca