fix: avoid race condition when spawning animated scenes with colliders (#101)

Unclear why this was triggering a race condition, as the `AnimatedScene`
asset should have a dependency on all subassets. This will fix it in the
short term while I don't have a more "proper" solution.

Perhaps I need to manually check the "recursive dependency load state"
using the asset server?

Author: mbrea-c

crates/bevy_animation_graph/src/core/animated_scene/mod.rs

@@ -90,7 +90,7 @@ pub(crate) fn spawn_animated_scenes(
 
         let processed_scene = if animscn.processed_scene.is_some() {
             animscn.processed_scene.as_ref().unwrap()
-        } else {
+        } else if is_scene_ready_to_process(animscn, &scenes, &skeletons, &skeleton_colliders) {
             let Some(scene) = scenes
                 .get(&animscn.source)
                 .and_then(|scn| scn.clone_with(&app_type_registry).ok())
@@ -111,6 +111,8 @@ pub(crate) fn spawn_animated_scenes(
 
             animscn.processed_scene = Some(scenes.add(scene));
             animscn.processed_scene.as_ref().unwrap()
+        } else {
+            continue;
         };
 
         commands
@@ -119,6 +121,22 @@ pub(crate) fn spawn_animated_scenes(
     }
 }
 
+/// Checks whether the scene can be processed
+fn is_scene_ready_to_process(
+    animscn: &AnimatedScene,
+    scenes: &Assets<Scene>,
+    skeletons: &Assets<Skeleton>,
+    skeleton_colliders: &Assets<SkeletonColliders>,
+) -> bool {
+    scenes.contains(&animscn.source)
+        && skeletons.contains(&animscn.skeleton)
+        && animscn.colliders.as_ref().is_none_or(|c| {
+            skeleton_colliders
+                .get(c)
+                .is_some_and(|c| skeletons.contains(&c.skeleton))
+        })
+}
+
 /// This function finds the [`bevy::animation::AnimationPlayer`] and replaces it with our own.
 ///
 /// It also applies retargeting if necessary.