[gnome-shell] overviewControls: Fix warning on shutdown

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

commit dc1aec5673183998128a1ce6251a39d16b0c8194
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Jul 8 20:42:55 2021 +0200

    overviewControls: Fix warning on shutdown
    
    ClutterActor unsets its layout manager's :container property during
    dispose, so the corresponding vfunc should handle being passed NULL.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1909>

 js/ui/overviewControls.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/js/ui/overviewControls.js b/js/ui/overviewControls.js
index 88726573dc..c153161696 100644
--- a/js/ui/overviewControls.js
+++ b/js/ui/overviewControls.js
@@ -112,7 +112,8 @@ class ControlsManagerLayout extends Clutter.BoxLayout {
 
     vfunc_set_container(container) {
         this._container = container;
-        this.hookup_style(container);
+        if (container)
+            this.hookup_style(container);
     }
 
     vfunc_get_preferred_width(_container, _forHeight) {