When a file has multiple tag frames mapping to the same logical tag
(e.g. both TXXX:MOOD and TMOO), TagLib merges them into one key with
multiple values. SplitTagValue had a len(values) != 1 guard that
skipped splitting entirely in this case, leaving comma-separated
values unsplit.
Change SplitTagValue to split each value individually regardless of
input count. Empty values are filtered during splitting.
Fixes#5065
ea4fe334e6