monitor-manager/native: Update assignments on empty-config too

Not doing so means we'll have whatever old assignments were there, which
can cause problems when e.g. newly generated output/crtc objects
automatically find old assignments.

Related: https://bugzilla.redhat.com/show_bug.cgi?id=2242612
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3318>

src/backends/native/meta-monitor-manager-native.c

@@ -286,6 +286,8 @@ meta_monitor_manager_native_apply_monitors_config (MetaMonitorManager        *ma
 
   if (!config)
     {
+      apply_crtc_assignments (manager, NULL, 0, NULL, 0);
+
       if (!manager->in_init)
         {
           MetaBackend *backend = meta_monitor_manager_get_backend (manager);