Return error when trying to print invalid ASN1 integer

Reviewed-by: NRich Salz <rsalz@openssl.org>
GH: #1322

crypto/asn1/tasn_prn.c

@@ -393,6 +393,8 @@ static int asn1_print_integer(BIO *out, ASN1_INTEGER *str)
     char *s;
     int ret = 1;
     s = i2s_ASN1_INTEGER(NULL, str);
+    if (s == NULL)
+        return 0;
     if (BIO_puts(out, s) <= 0)
         ret = 0;
     OPENSSL_free(s);