b4797956c7
Since commit 520cea9394, the opacity of icon grid children is used
both to skip children outside the current viewport and to hide the
real icons while animating icon clones.
As a result, a grid animation during an animation now ends up showing the
icons that are being animated. Avoid that glitch by leaving children's
opacity alone when there's an ongoing animation.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/582