Return directly NULL after ASN1_STRING_set, as it already has set an error code.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NKurt Roeckx <kurt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1074)