**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)
catch (const Exception & exc)
        {
            log->log(exc);
            packet_endpoint->sendPacket(ERRPacket(exc.code(), "00000", exc.message()), true);
        }
        OKPacket ok_packet(0, handshake_response.capability_flags, 0, 0, 0);
        packet_endpoint->sendPacket(ok_packet, true);
        while (true)
        {
            packet_endpoint->resetSequenceId();
            MySQLPacketPayloadReadBuffer payload = packet_endpoint->getPayload();
            char command = 0;
            payload.readStrict(command);
            
            LimitReadBuffer limited_payload(payload, 10000, true, "too long MySQL packet.");
            LOG_DEBUG(log, "Received command: {}. Connection id: {}.",
                static_cast<int>(static_cast<unsigned char>(command)), connection_id);
            try
            {
                switch (command)
                {
                    case COM_QUIT:
                        return;
                    case COM_INIT_DB:
                        comInitDB(limited_payload);
                        break;
                    case COM_QUERY:
                        comQuery(payload);
                        break;
                    case COM_FIELD_LIST: