FEC-14226: protect against case where tracks are not ready (#801)

### Description of the Changes

Please add a detailed description of the change, whether it's an
enhancement or a bugfix.
If the PR is related to an open issue please link to it.

### CheckLists

- [ ] changes have been done against master branch, and PR does not
conflict
- [ ] new unit / functional tests have been added (whenever applicable)
- [ ] test are passing in local environment
- [ ] Travis tests are passing (or test results are not worse than on
master branch :))
- [ ] Docs have been updated

src/player.ts

@@ -1445,7 +1445,7 @@ export default class Player extends FakeEventTarget {
    * @private
    */
   private _applyABRRestriction(config: any): void {
-    if (Utils.Object.hasPropertyPath(config, 'abr.restrictions') && this._engine && this._tracks.length) {
+    if (Utils.Object.hasPropertyPath(config, 'abr.restrictions') && this._engine && this._tracks?.length) {
       const { restrictions } = this._config.abr;
       const videoTracks: VideoTrack[] = <VideoTrack[]>this._tracks.filter((track) => track instanceof VideoTrack);
       const newVideoTracks = filterTracksByRestriction(videoTracks, restrictions);