WorkspaceManager/cleanup: Fix crash (#2292)

Co-authored-by: Leo <[email protected]>

Author: leolost2605

src/WorkspaceManager.vala

@@ -262,8 +262,18 @@ public class Gala.WorkspaceManager : Object {
     private void cleanup () {
         unowned Meta.WorkspaceManager manager = wm.get_display ().get_workspace_manager ();
 
-        foreach (var workspace in manager.get_workspaces ()) {
-            maybe_remove_workspace (workspace, null);
+        bool remove_last = false;
+        foreach (var workspace in manager.get_workspaces ().copy ()) {
+            if (Utils.get_n_windows (workspace, true) != 0) {
+                remove_last = false;
+                continue;
+            }
+
+            if (workspace.active) {
+                remove_last = true;
+            } else if (workspace.index () != manager.n_workspaces - 1 || remove_last) {
+                remove_workspace (workspace);
+            }
         }
     }
 }