**Describe the bug**
ClickHouse doesn't return affected rows via MySQL protocol for INSERT queries after 20.5+

**How to reproduce**
i create clear docker-compose environment for reproduce behavior MySQL + clickhouse + php + python
https://gist.github.com/Slach/aa67440ce856a3a53f64f92eeddfbc1b

**Queries to run that lead to unexpected result**
```
INSERT INTO default.t1(n) SELECT * FROM numbers(1000)
```

**Expected behavior**
MySQL protocol shall return affected rows field for INSERT queries (it works successful in 20.3 and 20.4)
![image](https://user-images.githubusercontent.com/105560/97867431-aa22ae00-1d2f-11eb-8caf-05431ffd29b3.png)

**Actual behavior**
![image](https://user-images.githubusercontent.com/105560/97867401-9f681900-1d2f-11eb-93cc-5ae6f1f5981b.png)
bool ssl_enabled, size_t connection_id_)
    : Poco::Net::TCPServerConnection(socket_)
    , server(server_)
    , log(&Poco::Logger::get("MySQLHandler"))
    , connection_context(server.context())
    , connection_id(connection_id_)
    , auth_plugin(new MySQLProtocol::Authentication::Native41())
{
    server_capability_flags = CLIENT_PROTOCOL_41 | CLIENT_SECURE_CONNECTION | CLIENT_PLUGIN_AUTH | CLIENT_PLUGIN_AUTH_LENENC_CLIENT_DATA | CLIENT_CONNECT_WITH_DB | CLIENT_DEPRECATE_EOF;
    if (ssl_enabled)
        server_capability_flags |= CLIENT_SSL;
    replacements.emplace("KILL QUERY", killConnectionIdReplacementQuery);
    replacements.emplace("SHOW TABLE STATUS LIKE", showTableStatusReplacementQuery);
    replacements.emplace("SHOW VARIABLES", selectEmptyReplacementQuery);
}
void MySQLHandler::run()
{
    connection_context.makeSessionContext();
    connection_context.setDefaultFormat("MySQLWire");
    in = std::make_shared<ReadBufferFromPocoSocket>(socket());
    out = std::make_shared<WriteBufferFromPocoSocket>(socket());
    packet_endpoint = std::make_shared<PacketEndpoint>(*in, *out, connection_context.mysql.sequence_id);
    try
    {