Fix empty player art when playing songs from favourites...

... or when playing songs from lists with directory content as mentioned in #4094 by adding full path to favourites for songs instead of musicdb path. 

before:
`<favourite name="song" thumb="folder.jpg">PlayMedia(&quot;musicdb://songs/1456.flac&quot;)</favourite>`
after:
`<favourite name="song" thumb="folder.jpg">PlayMedia(&quot;smb://<music_share>/<track>.flac&quot;)</favourite>`