**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)
```
zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/metadata", ReplicatedMergeTreeTableMetadata(*this, metadata_snapshot).toString(),
            zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/columns", metadata_snapshot->getColumns().toString(),
            zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/metadata_version", std::to_string(metadata_version),
            zkutil::CreateMode::Persistent));
        
        ops.emplace_back(zkutil::makeSetRequest(zookeeper_path + "/replicas", "last added replica: " + replica_name, replicas_stat.version));
        Coordination::Responses responses;
        code = zookeeper->tryMulti(ops, responses);
        if (code == Coordination::Error::ZNODEEXISTS)
        {
            throw Exception("Replica " + replica_path + " already exists.", ErrorCodes::REPLICA_IS_ALREADY_EXIST);
        }
        else if (code == Coordination::Error::ZBADVERSION)
        {
            LOG_ERROR(log, "Retrying createReplica(), because some other replicas were created at the same time");
        }
        else if (code == Coordination::Error::ZNONODE)
        {
            throw Exception("Table " + zookeeper_path + " was suddenly removed.", ErrorCodes::ALL_REPLICAS_LOST);
        }
        else
        {
            zkutil::KeeperMultiException::check(code, ops, responses);
        }
    } while (code == Coordination::Error::ZBADVERSION);
}
void StorageReplicatedMergeTree::drop()