Fix bug in strncpy() use of sk_ASN1_UTF8STRING2text() in asn1_lib.c

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/11300)
