Fix NETSCAPE_SPKI_print function to not assume NUL terminated strings

ASN.1 strings may not be NUL terminated. Don't assume they are.

CVE-2021-3712

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: David Benjamin <davidben@google.com>

crypto/asn1/t_spki.c

@@ -38,7 +38,7 @@ int NETSCAPE_SPKI_print(BIO *out, NETSCAPE_SPKI *spki)
     }
     chal = spki->spkac->challenge;
     if (chal->length)
-        BIO_printf(out, "  Challenge String: %s\n", chal->data);
+        BIO_printf(out, "  Challenge String: %.*s\n", chal->length, chal->data);
     i = OBJ_obj2nid(spki->sig_algor.algorithm);
     BIO_printf(out, "  Signature Algorithm: %s",
                (i == NID_undef) ? "UNKNOWN" : OBJ_nid2ln(i));