Incorrect highlighting of current track in audio player playlist

[quakerattled]

The audio player playlist does not highlight the correct song when it returns to the first song in the list. When it loops back to the first song, the last song remains highlighted. When the second song starts, the highlighting catches up and skips to the second song.

To replicate this problem:

• Upload 3 or more songs to the Media Library
• Create a new post -> Add Media -> Create Audio Playlist
• Add 3 or more songs to the playlist then "Insert audio playlist"
• Click publish
• Play the playlist to the end and let it loop back to the start

The problem occurs regardless of where you start in the playlist. I've tried it with the Twenty Twelve, Twenty Fourteen and Sorbet themes and can replicate it in all of them.

[wonderboymusic]

In 28649:

In WPPlaylistView::ended(), at the end of a playlist, set the index to 0 and call ->setCurrent() instead of ->loadCurrent() so that the first track is properly highlighted.

Fixes #28428.