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: NJiasheng Jiang <jiasheng@iscas.ac.cn>
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NPaul Dale <pauli@openssl.org>
Reviewed-by: NTomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17737)

crypto/x509/v3_utl.c

@@ -833,8 +833,11 @@ static int do_check_string(const ASN1_STRING *a, int cmp_type, equal_fn equal,
             rv = equal(a->data, a->length, (unsigned char *)b, blen, flags);
         else if (a->length == (int)blen && !memcmp(a->data, b, blen))
             rv = 1;
-        if (rv > 0 && peername)
+        if (rv > 0 && peername != NULL) {
             *peername = OPENSSL_strndup((char *)a->data, a->length);
+            if (*peername == NULL)
+                return -1;
+        }
     } else {
         int astrlen;
         unsigned char *astr;
@@ -847,8 +850,13 @@ static int do_check_string(const ASN1_STRING *a, int cmp_type, equal_fn equal,
             return -1;
         }
         rv = equal(astr, astrlen, (unsigned char *)b, blen, flags);
-        if (rv > 0 && peername)
+        if (rv > 0 && peername != NULL) {
             *peername = OPENSSL_strndup((char *)astr, astrlen);
+            if (*peername == NULL) {
+                OPENSSL_free(astr);
+                return -1;
+            }
+        }
         OPENSSL_free(astr);
     }
     return rv;