Avoid potential memory leak

Resolves #17827
Reviewed-by: NTomas Mraz <tomas@openssl.org>
Reviewed-by: NPaul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17828)

crypto/x509/v3_utl.c

@@ -539,8 +539,11 @@ static int append_ia5(STACK_OF(OPENSSL_STRING) **sk,
         return 0;
 
     emtmp = OPENSSL_strndup((char *)email->data, email->length);
-    if (emtmp == NULL)
+    if (emtmp == NULL) {
+        X509_email_free(*sk);
+        *sk = NULL;
         return 0;
+    }
 
     /* Don't add duplicates */
     if (sk_OPENSSL_STRING_find(*sk, emtmp) != -1) {