work around issue in MARC::Charset

work around issue in MARC::Charset

Because of a bug in MARC::Charset 0.98, if a string to convert from
MARC-8 to UTF-8 has (a) one or more diacritics that (b) are only in character positions
128 to 255 inclusive, the resulting converted string is not in
UTF-8, but the legacy 8-bit encoding (e.g., ISO-8859-1).  As a result,
when such a record is converted to XML using ->as_xml_record(), the resulting
XML can be truncated at the offending character.  An example of such a record
is one that has a price in Briish pounds in the 260$c but no other diacritics.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>