libmedia: Fixed bug on mix-encoded tag of Korean mp3s.

There are some Korean mp3s which not only one encoding used in their tag,
like album title in UTF-8 and everything else (like artist, title and etc)
in EUC-KR. and, only UTF-8 values was shown correctly.

Change-Id: Ie95efaf05ee4a08ee3859df0234fdd9ac3fbd413