[gnome-shell] altTab: Avoid setting GObject property to undefined instead of null

[Marge Bot <marge-bot src gnome org>]

commit b93bf2bd69a297e89f429fd8a71423105d43b7e9
Author: Sebastian Keller <skeller gnome org>
Date:   Fri Apr 23 16:10:52 2021 +0200

    altTab: Avoid setting GObject property to undefined instead of null
    
    The windowActor in the CyclerHighlight was set to undefined if
    this._window was null. This was causing an error when trying to set it
    as a property.
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/4167
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1820>

 js/ui/altTab.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/js/ui/altTab.js b/js/ui/altTab.js
index 3ecadad868..2ae7b6b232 100644
--- a/js/ui/altTab.js
+++ b/js/ui/altTab.js
@@ -427,7 +427,7 @@ class CyclerHighlight extends St.Widget {
         if (this._clone.source)
             this._clone.source.sync_visibility();
 
-        const windowActor = this._window?.get_compositor_private();
+        const windowActor = this._window?.get_compositor_private() ?? null;
 
         if (windowActor)
             windowActor.hide();