[gnome-shell] workspacesView: Make sure to destroy non-existing workspaces

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

commit 57f96b28ab50ec7b1d3ce6ba6e4d36124378c1b9
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Sep 29 13:38:40 2020 -0300

    workspacesView: Make sure to destroy non-existing workspaces
    
    Even if they're in the end of the list. So far we've managed to not be affected
    by this bug because until GNOME 3.38, workspaces didn't have a background, and
    there was no way to navigate to these leftover workspaces, but with the proposed
    overview changes for GNOME 40 it'll be very much visible.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1560>

 js/ui/workspacesView.js | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/js/ui/workspacesView.js b/js/ui/workspacesView.js
index 1e8faf3490..a7b3b878a9 100644
--- a/js/ui/workspacesView.js
+++ b/js/ui/workspacesView.js
@@ -222,6 +222,11 @@ class WorkspacesView extends WorkspacesViewBase {
             }
         }
 
+        for (let j = this._workspaces.length - 1; j >= newNumWorkspaces; j--) {
+            this._workspaces[j].destroy();
+            this._workspaces.splice(j, 1);
+        }
+
         this._updateScrollPosition();
     }