adding track to playlist (CLI) duplicates displayed comment tag info

[AF-1]

When you add a track to a playlist using

Slim::Control::Request::executeRequest(undef, ['playlists', 'edit', 'cmd:add', 'playlist_id:'.$playlistid, 'url:'.$trackURL]);

the comment tag of the added track (as displayed in the LMS context menu/song details)
goes from "EXAMPLESTRING" to "EXAMPESTRING / EXAMPLESTRING".
Furthermore, whenever you repeat the command yet another "/ EXAMPLESTRING" is appended.

The file tag info and the info in the LMS database comments table remain unchanged (=correct and not duplicated).

Might have sth to do with Slim::Schema::Track:comment.

[mherger]

More details in #781.