**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 part_path = replica_path + "/parts/" + part_name;
        exists_futures.emplace_back(zookeeper->asyncExists(part_path));
    }
    std::vector<std::future<Coordination::MultiResponse>> enqueue_futures;
    enqueue_futures.reserve(parts_to_fetch.size());
    for (size_t i = 0; i < parts_to_fetch.size(); ++i)
    {
        const String & part_name = parts_to_fetch[i];
        LOG_ERROR(log, "Removing locally missing part from ZooKeeper and queueing a fetch: {}", part_name);
        Coordination::Requests ops;
        time_t part_create_time = 0;
        Coordination::ExistsResponse exists_resp = exists_futures[i].get();
        if (exists_resp.error == Coordination::Error::ZOK)
        {
            part_create_time = exists_resp.stat.ctime / 1000;
            removePartFromZooKeeper(part_name, ops, exists_resp.stat.numChildren > 0);
        }
        LogEntry log_entry;
        log_entry.type = LogEntry::GET_PART;
        log_entry.source_replica = "";
        log_entry.new_part_name = part_name;
        log_entry.create_time = part_create_time;
        
        ops.emplace_back(zkutil::makeCreateRequest(
            replica_path + "/queue/queue-", log_entry.toString(), zkutil::CreateMode::PersistentSequential));
        enqueue_futures.emplace_back(zookeeper->asyncMulti(ops));
    }
    for (auto & future : enqueue_futures)
        future.get();