Fix a crash in the asn1parse command

Thanks to Sem Voigtländer for reporting this issue.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/5826)

(cherry picked from commit 752837e0)