Skip zero-length subfields for ISO2709.
Skip zero-length subfields for ISO2709.

Skip zero-length subfields when decoding ISO2709. This rare case happens
if a record has two FS characters in a sequence. Without this patch
there would be a reference beyond char array in using_code_len fragments
in marcdisp.c.

nla/yaz,nla/yaz,dcrossleyau/yaz,dcrossleyau/yaz,nla/yaz,dcrossleyau/yaz,nla/yaz