**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)
copyData(*packet_endpoint->in, buf_for_handshake_response, packet_size - pos);
        ReadBufferFromString payload(buf_for_handshake_response.str());
        payload.ignore(PACKET_HEADER_SIZE);
        packet.readPayloadWithUnpacked(payload);
        packet_endpoint->sequence_id++;
    }
}
void MySQLHandler::authenticate(const String & user_name, const String & auth_plugin_name, const String & initial_auth_response)
{
    try
    {
        
        auto user = connection_context.getAccessControlManager().read<User>(user_name);
        const DB::Authentication::Type user_auth_type = user->authentication.getType();
        if (user_auth_type == DB::Authentication::SHA256_PASSWORD)
        {
            authPluginSSL();
        }
        std::optional<String> auth_response = auth_plugin_name == auth_plugin->getName() ? std::make_optional<String>(initial_auth_response) : std::nullopt;
        auth_plugin->authenticate(user_name, auth_response, connection_context, packet_endpoint, secure_connection, socket().peerAddress());
    }
    catch (const Exception & exc)
    {
        LOG_ERROR(log, "Authentication for user {} failed.", user_name);
        packet_endpoint->sendPacket(ERRPacket(exc.code(), "00000", exc.message()), true);
        throw;
    }
    LOG_DEBUG(log, "Authentication for user {} succeeded.", user_name);
}
void MySQLHandler::comInitDB(ReadBuffer & payload)