wolfssl: Reject EC keys with explicitly encoded parameters

These are not allowed in X.509 certificates according to RFC 5480 and
some newer validations apparently explicitly check for this.

Note that WolfSSL rejects such keys, by default.  Only when compiled with
WOLFSSL_NO_ASN_STRICT are they accepted.

src/libstrongswan/plugins/wolfssl/wolfssl_ec_private_key.c

@@ -449,7 +449,8 @@ wolfssl_ec_private_key_t *wolfssl_ec_private_key_load(key_type_t type,
 	}
 
 	idx = 0;
-	if (wc_EccPrivateKeyDecode(key.ptr, &idx, &this->ec, key.len) < 0)
+	if (wc_EccPrivateKeyDecode(key.ptr, &idx, &this->ec, key.len) < 0 ||
+		this->ec.idx == -1)
 	{
 		destroy(this);
 		return NULL;

src/libstrongswan/plugins/wolfssl/wolfssl_ec_public_key.c

@@ -378,7 +378,7 @@ wolfssl_ec_public_key_t *wolfssl_ec_public_key_load(key_type_t type,
 
 	idx = 0;
 	ret = wc_EccPublicKeyDecode(blob.ptr, &idx, &this->ec, blob.len);
-	if (ret < 0)
+	if (ret < 0 || this->ec.idx == -1)
 	{
 		destroy(this);
 		return NULL;