**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)
```
}
    
    Strings source_queue_names;
    
    
    while (true)
    {
        Coordination::Stat log_pointer_stat;
        String raw_log_pointer = zookeeper->get(source_path + "/log_pointer", &log_pointer_stat);
        Coordination::Requests ops;
        ops.push_back(zkutil::makeSetRequest(replica_path + "/log_pointer", raw_log_pointer, -1));
        
        if (source_is_lost_stat.version == -1)
        {
            
            
            ops.push_back(zkutil::makeCreateRequest(source_path + "/is_lost", "0", zkutil::CreateMode::Persistent));
            ops.push_back(zkutil::makeRemoveRequest(source_path + "/is_lost", -1));
        }
        else 
            ops.push_back(zkutil::makeCheckRequest(source_path + "/is_lost", source_is_lost_stat.version));
        Coordination::Responses responses;
        
        source_queue_names = zookeeper->getChildren(source_path + "/queue");
        
        ops.push_back(zkutil::makeCheckRequest(source_path + "/log_pointer", log_pointer_stat.version));
        auto rc = zookeeper->tryMulti(ops, responses);
        if (rc == Coordination::Error::ZOK)
        {
            break;