When searching MIME body headers, make sure we don't go out of bounds with broken MIME messages and cause assert-crash.
When searching MIME body headers, make sure we don't go out of bounds with broken MIME messages and cause assert-crash.

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot