End loop if length check fails

An infinite loop occurs in this file: https://www.wireshark.org/download/automated/captures/fuzz-2009-06-27-18328.pcap

Specifically this http field causes the problem:
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; MS Web Services Client Protocol 2.0.50727.143;)

The ';' at the end causes the loop to recognize a length failure, but the loop continues since comment_begin isn't set to null.