wayland: Plug leak in error condition

If we fail to bind the X11 socket, free the lock file string.

CID: #1505865
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2061>

src/wayland/meta-xwayland.c

@@ -777,6 +777,7 @@ choose_xdisplay (MetaXWaylandManager     *manager,
             {
               g_prefix_error (&local_error, "Failed to bind X11 socket: ");
               g_propagate_error (error, g_steal_pointer (&local_error));
+              g_free (lock_file);
               return FALSE;
             }