Don't crash if SORT elements don't contain headers.
Don't crash if SORT elements don't contain headers.

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