**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)
```
Coordination::Requests ops;
    Coordination::Responses responses;
    ops.emplace_back(zkutil::makeCreateRequest(
        zookeeper_path + "/log/log-", entry.toString(),
        zkutil::CreateMode::PersistentSequential));
    ops.emplace_back(zkutil::makeSetRequest(
        zookeeper_path + "/log", "", log_version)); 
    Coordination::Error code = zookeeper->tryMulti(ops, responses);
    if (code == Coordination::Error::ZBADVERSION)
    {
        ProfileEvents::increment(ProfileEvents::NotCreatedLogEntryForMutation);
        LOG_TRACE(log, "Log entry is not created for mutation {} because log was updated", new_part_name);
        return CreateMergeEntryResult::LogUpdated;
    }
    zkutil::KeeperMultiException::check(code, ops, responses);
    ProfileEvents::increment(ProfileEvents::CreatedLogEntryForMutation);
    LOG_TRACE(log, "Created log entry for mutation {}", new_part_name);
    return CreateMergeEntryResult::Ok;
}
void StorageReplicatedMergeTree::removePartFromZooKeeper(const String & part_name, Coordination::Requests & ops, bool has_children)
{
    String part_path = replica_path + "/parts/" + part_name;
    if (has_children)
    {
        ops.emplace_back(zkutil::makeRemoveRequest(part_path + "/checksums", -1));
        ops.emplace_back(zkutil::makeRemoveRequest(part_path + "/columns", -1));
    }
    ops.emplace_back(zkutil::makeRemoveRequest(part_path, -1));
}
void StorageReplicatedMergeTree::removePartAndEnqueueFetch(const String & part_name)