2a0c116757
When using the fade animation when transitioning to the overview instead
of zoom, we fade out all window previews to fully transparent. But after
commit 751189253a removed the old _updateWindowPositions() function,
nothing resets the opacity again, so when switching from the app- to the
window picker, all previews are hidden.
Fix this by always resetting the window preview opacity after showing
or hiding the overview.
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2969