Reject multi-byte encodings with no converter function.
Reject multi-byte encodings with no converter function.

Not supplying a character encoding convert function when one was
needed previously caused a segfault if a multi-byte character was
encountered.  This errors at the start of parse instead.

libexpat/libexpat,libexpat/libexpat,libexpat/libexpat,libexpat/libexpat,libexpat/libexpat,libexpat/libexpat