**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)
```
for (size_t i = 0; i < part_names.size(); ++i)
        {
            Coordination::ExistsResponse exists_resp = exists_futures[i].get();
            if (exists_resp.error == Coordination::Error::ZOK)
            {
                Coordination::Requests ops;
                removePartFromZooKeeper(part_names[i], ops, exists_resp.stat.numChildren > 0);
                remove_futures.emplace_back(zookeeper->tryAsyncMulti(ops));
            }
            else
            {
                LOG_DEBUG(log, "There is no part {} in ZooKeeper, it was only in filesystem", part_names[i]);
                
                remove_futures.emplace_back();
            }
        }
    }
    catch (const Coordination::Exception & e)
    {
        if (parts_should_be_retried && Coordination::isHardwareError(e.code))
            parts_should_be_retried->insert(part_names.begin(), part_names.end());
        throw;
    }
    for (size_t i = 0; i < remove_futures.size(); ++i)
    {
        auto & future = remove_futures[i];
        if (!future.valid())
            continue;
        auto response = future.get();
        if (response.error == Coordination::Error::ZOK)