Fix root surface tracking for sync subsurfaces

In particular, fixes screenshot-window with show-pointer on foot CSD.

src/handlers/compositor.rs

@@ -62,10 +62,6 @@ impl CompositorHandler for State {
         on_commit_buffer_handler::<Self>(surface);
         self.backend.early_import(surface);
 
-        if is_sync_subsurface(surface) {
-            return;
-        }
-
         let mut root_surface = surface.clone();
         while let Some(parent) = get_parent(&root_surface) {
             root_surface = parent;
@@ -76,6 +72,10 @@ impl CompositorHandler for State {
             .root_surface
             .insert(surface.clone(), root_surface.clone());
 
+        if is_sync_subsurface(surface) {
+            return;
+        }
+
         if surface == &root_surface {
             // This is a root surface commit. It might have mapped a previously-unmapped toplevel.
             if let Entry::Occupied(entry) = self.niri.unmapped_windows.entry(surface.clone()) {