Fixed not increment mediaIndex when segmentXhr_ is aborted in setCurrentTime

When I call setCurrentTime(seconds), the player wouldn't seek the specified value since mediaIndex is wrong (then, next segment file would be sought). It seems mediaindex is incremented when segmentXhr_ is aborted.

```javascript
videojs.Hls.prototype.loadSegment = function(segmentUri, offset) {
    ...
    if (error) {
      // if a segment request times out, we may have better luck with another playlist
      if (error === 'timeout') {
        tech.bandwidth = 1;
        return tech.playlists.media(tech.selectPlaylist());
      }
      // otherwise, try jumping ahead to the next segment
      tech.error = {
        status: this.status,
        message: 'HLS segment request error at URL: ' + url,
        code: (this.status >= 500) ? 4 : 2
      };

      // try moving on to the next segment
      tech.mediaIndex++;
      return;
    }
```