bugfix: DEFAULT=YES on caption tracks was not being respected.

Reason for this was because the subtitle grouping wasn't populating the
tracks before the findTrackId function was called. So, it was looking
over an empty array on the first invocation of the function.

By moving it, it now has the correct behaviour and the default track is
selected.

Closes #3780.

src/controller/subtitle-track-controller.ts

@@ -191,13 +191,15 @@ class SubtitleTrackController extends BasePlaylistController {
       const lastTrack = this.tracksInGroup
         ? this.tracksInGroup[this.trackId]
         : undefined;
-      const initialTrackId =
-        this.findTrackId(lastTrack?.name) || this.findTrackId();
+
       const subtitleTracks = this.tracks.filter(
         (track): boolean => !textGroupId || track.groupId === textGroupId
       );
-      this.groupId = textGroupId;
       this.tracksInGroup = subtitleTracks;
+      const initialTrackId =
+        this.findTrackId(lastTrack?.name) || this.findTrackId();
+      this.groupId = textGroupId;
+
       const subtitleTracksUpdated: SubtitleTracksUpdatedData = {
         subtitleTracks,
       };
@@ -213,9 +215,9 @@ class SubtitleTrackController extends BasePlaylistController {
   }
 
   private findTrackId(name?: string): number {
-    const audioTracks = this.tracksInGroup;
-    for (let i = 0; i < audioTracks.length; i++) {
-      const track = audioTracks[i];
+    const textTracks = this.tracksInGroup;
+    for (let i = 0; i < textTracks.length; i++) {
+      const track = textTracks[i];
       if (!this.selectDefaultTrack || track.default) {
         if (!name || name === track.name) {
           return track.id;