Don't crash when extension header is resized and there are extensions after it.
Don't crash when extension header is resized and there are extensions after
it.

Distrotech/dovecot,LTD-Beget/dovecot,damoxc/dovecot,damoxc/dovecot,Distrotech/dovecot,damoxc/dovecot,Distrotech/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,Distrotech/dovecot,damoxc/dovecot,Distrotech/dovecot,LTD-Beget/dovecot,damoxc/dovecot