Bug: Race condition in handleTechSourceset_() async callback #9187

if (!event.src) {
  this.tech_.any(['sourceset', 'loadstart'], (e) => {
    if (e.type === 'sourceset') {
      return;
    }
    const techSrc = this.techGet_('currentSrc');  // <-- tech_ may be false
    this.lastSource_.tech = techSrc;               // <-- lastSource_ may be invalid
    this.updateSourceCaches_(techSrc);
  });
}

this.tech_.any(['sourceset', 'loadstart'], (e) => {
  if (!this.tech_ || e.type === 'sourceset') {
    return;
  }
  // ...
});