At the end of BaseAppView._clearAnimateLater(), the '_grid' actor's opacity is
set to 255. As it turns out, _clearAnimateLater() is called, among others, by
vfunc_unmap(). However, unmapping is part of the destruction process, and at
the time it is called, '_grid' is already destroying, which makes GJS complain
about accessing an invalid object.
Don't change opacity on BaseAppView._clearAnimateLater(), and instead move it
to the couple of places outside vfunc_unmap() that call it.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1447
33bd038af2