**Describe the bug**
The ClickHouse client freezes when executing `ALTER TABLE` with `ADD COLUMN` and `MODIFY ORDER` on a table built using Replicated Versioned Collapsing Merge Tree engine.

**How to reproduce**
* ClickHouse client version 20.10.1.1.
Connecting to localhost:9000 as user default.
Connected to ClickHouse server version 20.10.1 revision 54440.

* `CREATE TABLE` statements
```
SHOW CREATE TABLE table0

┌─statement──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE TABLE default.table0
(
    `d` Date,
    `a` String,
    `b` UInt8,
    `x` String,
    `y` Int8,
    `version` UInt64,
    `sign` Int8 DEFAULT 1
)
ENGINE = ReplicatedVersionedCollapsingMergeTree('/clickhouse/tables/{shard}/table0', '{replica}', sign, version)
PARTITION BY y
ORDER BY d
SETTINGS index_granularity = 8192 │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

1 rows in set. Elapsed: 0.004 sec.
```

* Queries to run that lead to unexpected result
```
ALTER TABLE table0 ADD COLUMN order UInt32, MODIFY ORDER BY (d, order)
```
String log_entry_str;
            bool exists = getZooKeeper()->tryGet(zookeeper_path + "/log/" + log_entry_name, log_entry_str);
            if (exists && entry_str == log_entry_str)
            {
                found = true;
                log_node_name = log_entry_name;
                break;
            }
        }
        if (found)
        {
            LOG_DEBUG(log, "Waiting for {} to pull {} to queue", replica, log_node_name);
            
            while (!stop_waiting())
            {
                zkutil::EventPtr event = std::make_shared<Poco::Event>();
                String log_pointer_new = getZooKeeper()->get(zookeeper_path + "/replicas/" + replica + "/log_pointer", nullptr, event);
                if (!log_pointer_new.empty() && parse<UInt64>(log_pointer_new) > log_index)
                    break;
                if (wait_for_non_active)
                    event->wait();
                else
                    event->tryWait(event_wait_timeout_ms);
            }
        }
    }
    else
        throw Exception("Logical error: unexpected name of log node: " + entry.znode_name, ErrorCodes::LOGICAL_ERROR);
    if (!log_node_name.empty())
        LOG_DEBUG(log, "Looking for node corresponding to {} in {} queue", log_node_name, replica);