workspace: Sanity check input to activate*()

The passed argument should be a workspace, and it should not have been
removed.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2707>

src/core/workspace.c

@@ -577,6 +577,9 @@ meta_workspace_activate_with_focus (MetaWorkspace *workspace,
   gint num_workspaces, current_space, new_space;
   MetaMotionDirection direction;
 
+  g_return_if_fail (META_IS_WORKSPACE (workspace));
+  g_return_if_fail (meta_workspace_index (workspace) != -1);
+
   meta_verbose ("Activating workspace %d",
                 meta_workspace_index (workspace));