macos: maintain GList element consistency

We need to keep this consistent so that we can look things up
faster in other places. Therefore, just take the hit here and clear
the entire list ensuring prev/next poniters are cleared.

gdk/macos/gdkmacosdisplay.c

@@ -1056,9 +1056,8 @@ _gdk_macos_display_clear_sorting (GdkMacosDisplay *self)
 {
   g_return_if_fail (GDK_IS_MACOS_DISPLAY (self));
 
-  self->sorted_surfaces.head = NULL;
-  self->sorted_surfaces.tail = NULL;
-  self->sorted_surfaces.length = 0;
+  while (self->sorted_surfaces.head != NULL)
+    g_queue_unlink (&self->sorted_surfaces, self->sorted_surfaces.head);
 }
 
 const GList *