**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)
```
{
    auto zookeeper = tryGetZooKeeper();
    const auto storage_settings_ptr = getSettings();
    res.is_leader = is_leader;
    res.can_become_leader = storage_settings_ptr->replicated_can_become_leader;
    res.is_readonly = is_readonly;
    res.is_session_expired = !zookeeper || zookeeper->expired();
    res.queue = queue.getStatus();
    res.absolute_delay = getAbsoluteDelay(); 
    res.parts_to_check = part_check_thread.size();
    res.zookeeper_path = zookeeper_path;
    res.replica_name = replica_name;
    res.replica_path = replica_path;
    res.columns_version = -1;
    res.log_max_index = 0;
    res.log_pointer = 0;
    res.total_replicas = 0;
    res.active_replicas = 0;
    if (with_zk_fields && !res.is_session_expired)
    {
        try
        {
            auto log_entries = zookeeper->getChildren(zookeeper_path + "/log");