Also change IcyInfo.rawMetatadata from String to byte[]
ICY doesn't specify the character encoding, and there are streams
not using UTF-8 (issue:#6753). It seems the default of at least one
server is ISO-8859-1 so let's support that as a fallback:
https://github.com/savonet/liquidsoap/issues/411#issuecomment-288759200
Also update IcyDecoder to skip strings it doesn't recognise at all
instead of decoding invalid characters.
The feed from issue:#6753 now decodes accents correctly:
EventLogger: ICY: title="D Pai - Le temps de la rentrée", url="null"
PiperOrigin-RevId: 285388522
