**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 = getZooKeeper();
    String part_path = replica_path + "/parts/" + part_name;
    Coordination::Requests ops;
    time_t part_create_time = 0;
    Coordination::Stat stat;
    if (zookeeper->exists(part_path, &stat))
    {
        part_create_time = stat.ctime / 1000;
        removePartFromZooKeeper(part_name, ops, stat.numChildren > 0);
    }
    LogEntryPtr log_entry = std::make_shared<LogEntry>();
    log_entry->type = LogEntry::GET_PART;
    log_entry->create_time = part_create_time;
    log_entry->source_replica = "";
    log_entry->new_part_name = part_name;
    ops.emplace_back(zkutil::makeCreateRequest(
        replica_path + "/queue/queue-", log_entry->toString(),
        zkutil::CreateMode::PersistentSequential));
    auto results = zookeeper->multi(ops);
    String path_created = dynamic_cast<const Coordination::CreateResponse &>(*results.back()).path_created;
    log_entry->znode_name = path_created.substr(path_created.find_last_of('/') + 1);
    queue.insert(zookeeper, log_entry);
}
void StorageReplicatedMergeTree::enterLeaderElection()