Fix print of ASN.1 BIGNUM type.
Fix print of ASN.1 BIGNUM type.

The ASN.1 BIGNUM type needs to be handled in a custom way as it is
not a generic ASN1_STRING type.

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl