Merge tags instead of replacing when dynamically updating song tags from remote stream

[geneticdrift]

issue #1400

Tested with this playlist for remote stream with tags:

<?xml version="1.0" encoding="UTF-8"?>
<playlist version="1" xmlns="http://xspf.org/ns/0/">
  <trackList>
    <track>
        <location>http://live02.rfi.fr/rfimonde-64.mp3</location>
        <title>RFI Monde</title>
        <album>French international radio</album>
        <creator>French Radio</creator>
        <annotation>French listening</annotation>
        <trackNum>1</trackNum>
    </track>
  </trackList>
</playlist>

Before change local tags are gone when playback starts:

OK MPD 0.24.0
playlistinfo 0:1
file: http://live02.rfi.fr/rfimonde-64.mp3
Title: RFI Monde
Album: French international radio
Artist: French Radio
Comment: French listening
Track: 1
Pos: 0
Id: 2
OK
play
OK
playlistinfo 0:1
file: http://live02.rfi.fr/rfimonde-64.mp3
Name: RFI monde 64
Pos: 0
Id: 2
OK

After change local tags are preserved when playback starts:

OK MPD 0.24.0
playlistinfo 0:1
file: http://live02.rfi.fr/rfimonde-64.mp3
Title: RFI Monde
Album: French international radio
Artist: French Radio
Comment: French listening
Track: 1
Pos: 0
Id: 2
OK
play
OK
playlistinfo 0:1
file: http://live02.rfi.fr/rfimonde-64.mp3
Name: RFI monde 64
Title: RFI Monde
Album: French international radio
Artist: French Radio
Comment: French listening
Track: 1
Pos: 0
Id: 2
OK

[geneticdrift]

Should I close this?