**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 entry;
        if (!zookeeper->tryGet(source_path + "/queue/" + entry_name, entry))
            continue;
        source_queue.push_back(entry);
    }
    
    Strings source_replica_parts = zookeeper->getChildren(source_path + "/parts");
    ActiveDataPartSet active_parts_set(format_version, source_replica_parts);
    Strings active_parts = active_parts_set.getParts();
    
    Strings local_parts_in_zk = zookeeper->getChildren(replica_path + "/parts");
    Strings parts_to_remove_from_zk;
    for (const auto & part : local_parts_in_zk)
    {
        if (active_parts_set.getContainingPart(part).empty())
        {
            queue.remove(zookeeper, part);
            parts_to_remove_from_zk.emplace_back(part);
            LOG_WARNING(log, "Source replica does not have part {}. Removing it from ZooKeeper.", part);
        }
    }
    tryRemovePartsFromZooKeeperWithRetries(parts_to_remove_from_zk);
    auto local_active_parts = getDataParts();
    DataPartsVector parts_to_remove_from_working_set;
    for (const auto & part : local_active_parts)
    {
        if (active_parts_set.getContainingPart(part->name).empty())
        {
            parts_to_remove_from_working_set.emplace_back(part);
            LOG_WARNING(log, "Source replica does not have part {}. Removing it from working set.", part->name);