g-w-l/workspace-switcher: Fix random crash and errors when adding

and removing workspaces.

gwl: Remove workspaces last-to-first when removing so the removal
of lower-index workspaces won't affect the position of higher
ones while they're being destroyed.

workspace-switcher: Connect to 'workspaces-reordered', not
'workareas-changed', and perform a button refresh immediately
when receiving these signals.

The workareas-changed signal only fires from one place that the
n_workspaces property notify is not, and it's also on an idle
callback inside of muffin, so by the time workareas-changed got
sent, the situation could have already changed, plus it would be
the second signal received for the change (n_workspaces being
updated immediately).

The workspaces-reordered is called in that single instance that
n_workspaces is not, so connect to that instead, since it's also
immediate.

ref:
linuxmint/muffin@603dba89297695a53fe9
linuxmint/mint21-beta#89

Author: mtwebster

files/usr/share/cinnamon/applets/[email protected]/applet.js

@@ -922,14 +922,16 @@ class GroupedWindowListApplet extends Applet.Applet {
         for (let i = 0; i < this.appLists.length; i++) {
             let workspaceIndex = this.appLists[i].metaWorkspace.index();
             if (workspaceIndex === -1) {
-                this.appLists[i].destroy();
-                this.appLists[i] = null;
+                if (this.appLists[i] != null) {
+                    this.appLists[i].destroy();
+                    this.appLists[i] = null;
+                }
                 removedLists.push(i);
             } else {
                 this.appLists[i].index = workspaceIndex;
             }
         }
-        for (let i = 0; i < removedLists.length; i++) {
+        for (let i = removedLists.length - 1; i >= 0; i--) {
             this.appLists.splice(removedLists[i], 1);
         }
         this.state.set({currentWs: global.screen.get_active_workspace_index()});

files/usr/share/cinnamon/applets/[email protected]/applet.js

@@ -283,8 +283,8 @@ class CinnamonWorkspaceSwitcher extends Applet.Applet {
         this.actor.connect('scroll-event', this.hook.bind(this));
 
         this.queueCreateButtons();
-        global.screen.connect('notify::n-workspaces', Lang.bind(this, this.onNumberOfWorkspacesChanged));
-        global.screen.connect('workareas-changed', Lang.bind(this, this.queueCreateButtons));
+        global.workspace_manager.connect('notify::n-workspaces', () => { this.onWorkspacesUpdated() });
+        global.workspace_manager.connect('workspaces-reordered', () => { this.onWorkspacesUpdated() });
         global.window_manager.connect('switch-workspace', this._onWorkspaceChanged.bind(this));
         global.settings.connect('changed::panel-edit-mode', Lang.bind(this, this.on_panel_edit_mode_changed));
 
@@ -311,7 +311,7 @@ class CinnamonWorkspaceSwitcher extends Applet.Applet {
 
     onNumberOfWorkspacesChanged() {
         this.removeWorkspaceMenuItem.setSensitive(global.screen.n_workspaces > 1);
-        this.queueCreateButtons();
+        this._createButtons();
     }
 
     removeWorkspace  (){