Safari failing Load Graph tests

[joeyparrish]

Safari 15.4 (Mac OS 10.15.7) Player Load Graph routing goes from load to src equals FAILED
        TypeError: null is not an object (evaluating 'this.video_.textTracks') thrown
        TypeError: null is not an object (evaluating 'this.video_.textTracks') thrown

It appears that this code is to blame in lib/player.js:

  processChaptersTrack_(track) {
    if (!track || track.kind != 'chapters') {
      return;
    }

    // Hidden mode is required for the cuechange event to launch correctly and
    // get the cues and the activeCues
    track.mode = 'hidden';

    // In Safari the initial assignment does not always work, so we schedule
    // this process to be repeated several times to ensure that it has been put
    // in the correct mode.
    new shaka.util.Timer(() => {
      const chaptersTracks = this.getChaptersTracks_();
      for (const chaptersTrack of chaptersTracks) {
        chaptersTrack.mode = 'hidden';
      }
    }).tickNow().tickAfter(/* seconds= */ 0.5);
  }

When the timer fires, the player has already been destroyed.