Callbacks: fix addCallbackOrWaitCollectionAvailable() when providing concrete class

Author: endel

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@colyseus/schema",
-  "version": "4.0.10",
+  "version": "4.0.11",
   "description": "Binary state serializer with delta encoding for games",
   "type": "module",
   "bin": {

src/decoder/strategy/Callbacks.ts

@@ -85,7 +85,7 @@ export class StateCallbackStrategy<TState extends IRef> {
         const collection = (instance as any)[propertyName] as TReturn;
 
         // Collection not available yet. Listen for its availability before attaching the handler.
-        if (collection === null || collection === undefined) {
+        if (!collection || collection[$refId] === undefined) {
             removeHandler = this.addCallback(
                 instance[$refId],
                 propertyName,