Parsing local file tags will fail if ffprobe JSON keys are non-lowercase

[metaisfacil]

Title says it all. If, for instance, a FLAC has the artist name stored in the "ARTIST" tag and not specifically "artist", ffprobe will report the tags with case intact - and the saveSong() routine will simply skip over the track as "no title found in metadata". The same applies to all other metadata fields.

A potential fix could be to force all the keys in the JSON returned by wav.GetMetadata() to be lowercase, although that could cause issues on its own of course.