Turning off subtitling is not clean

Created by: TobbeMobiTV

setTextTrack in TextSourceBuffer loops over text tracks as there is a change. If a new track is in mode "showing", it tidies up things and clears the old track. However, it does not do anything when there is no longer any track showing.

I think the code should rather look something like below, but I lack the proper call to the mediaController to tell that there is no track active right now, so I haven't made a PR.

   setTextTrack = function() {
        var el = this.videoModel.getElement(),
            tracks = el.textTracks,
            ln = tracks.length,
            self = this,
            previousTrackIdx = self.textTrackExtensions.getCurrentTrackIdx(),
            newTrackIdx = -1;

        for (var i = 0; i < ln; i++ ) {
            var track = tracks[i];
            if (track.mode === "showing") {
                newTrackIdx = i;
                break;
            }
        }
        console.log("TOBBE index " + previousTrackIdx + " " + newTrackIdx);
        if (newTrackIdx !== previousTrackIdx) {
            if (previousTrackIdx !== -1) {
                var previousTextTrack = tracks[previousTrackIdx];
                if (previousTextTrack !== null) {
                    self.textTrackExtensions.deleteTrackCues(previousTextTrack);
                    if (previousTextTrack.renderingType === "html") {
                        self.textTrackExtensions.removeNativeCueStyle();
                        self.textTrackExtensions.clearCues();
                    }
                }
                self.fragmentModel.cancelPendingRequests();
                self.fragmentModel.abortRequests();
                self.buffered.clear();
            }
            self.textTrackExtensions.setCurrentTrackIdx(newTrackIdx);
            if (newTrackIdx !== -1) {
                self.mediaController.setTrack(self.allTracks[newTrackIdx]);
            } else  {
               // I'm missing the right thing to do here to tell the mediaController that no track is active
            }
        }
    };