Unable to select text track with no ROLES ( v 2.3.0 )

[kchandran1029]

No way to select a text track that has empty roles when there is another track for same language that has non-empty roles.

Version : 2.3.0

Input code

// this sets currentTextRole_ to empty.
shakaPlayer.selectTextLanguage(this.textTracks[trackId].language, '');
shakaPlayer.setTextTrackVisibility(true);

// Now refine the choice based on role preference.
if (preferredRole) { // Kiran : This won't be true for empty role preference
  var roleMatches = shaka.util.StreamUtils.filterTextStreamsByRole_(
      chosen, preferredRole);
  if (roleMatches.length) {
    return roleMatches;
  } else {
    shaka.log.warning('No exact match for the text role could be found.');
  }
}

Then ,

// Either there was no role preference, or it could not be satisfied.
// Choose an arbitrary role, if there are any, and filter out any other roles.
// This ensures we never adapt between roles.

var allRoles = chosen.map(function(stream) {
  return stream.roles;
}).reduce(shaka.util.Functional.collapseArrays, []);

// Kiran: This will return the stream that has non empty ROLE.

Expected behavior
should return the first track that matches the language as well as exact role, if role preference is empty , should return the track where roles.length === 0.

Current behavior
Always returns the non-empty role text track.

[joeyparrish]

Cherry-picked to v2.3.1.