
We're calculating icon sizes for the alt tab switcher early and at a
point where the style attributes of this._list are not loaded yet. To
make sure the value of this._list.spacing is correct, call
ensure_style() on this._list before accessing the spacing.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/587
(cherry picked from commit eab320dab5
)