crypto/x509/v3_utl.c: Add missing check for OPENSSL_strndup

crypto/x509/v3_utl.c: Add missing check for OPENSSL_strndup

Since the potential failure of memory allocation, it
should be better to check the return value of the
OPENSSL_strndup(), like x509v3_add_len_value().
And following the comment of 'if (astrlen < 0)',
return -1 if fails.

Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17737)