**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 source_replica;
    Coordination::Stat source_is_lost_stat;
    size_t future_num = 0;
    for (const String & source_replica_name : replicas)
    {
        if (source_replica_name == replica_name)
            continue;
        auto get_is_lost     = futures[future_num++].get();
        auto get_log_pointer = futures[future_num++].get();
        auto get_queue       = futures[future_num++].get();
        if (get_is_lost.error != Coordination::Error::ZOK)
        {
            LOG_INFO(log, "Not cloning {}, cannot get '/is_lost': {}", Coordination::errorMessage(get_is_lost.error));
            continue;
        }
        else if (get_is_lost.data != "0")
        {
            LOG_INFO(log, "Not cloning {}, it's lost");
            continue;
        }
        if (get_log_pointer.error != Coordination::Error::ZOK)
        {
            LOG_INFO(log, "Not cloning {}, cannot get '/log_pointer': {}", Coordination::errorMessage(get_log_pointer.error));
            continue;
        }
        if (get_queue.error != Coordination::Error::ZOK)
        {
            LOG_INFO(log, "Not cloning {}, cannot get '/queue': {}", Coordination::errorMessage(get_queue.error));
            continue;
        }