**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;
            if (!is_parallel)
            {
                Coordination::Stat added_parts_stat;
                String old_added_parts = zookeeper->get(quorum_last_part_path, &added_parts_stat);
                ReplicatedMergeTreeQuorumAddedParts parts_with_quorum(format_version);
                if (!old_added_parts.empty())
                    parts_with_quorum.fromString(old_added_parts);
                auto part_info = MergeTreePartInfo::fromPartName(part_name, format_version);
                
                parts_with_quorum.added_parts[part_info.partition_id] = part_name;
                String new_added_parts = parts_with_quorum.toString();
                ops.emplace_back(zkutil::makeRemoveRequest(quorum_status_path, stat.version));
                ops.emplace_back(zkutil::makeSetRequest(quorum_last_part_path, new_added_parts, added_parts_stat.version));
            }
            else
                ops.emplace_back(zkutil::makeRemoveRequest(quorum_status_path, stat.version));
            auto code = zookeeper->tryMulti(ops, responses);
            if (code == Coordination::Error::ZOK)
            {
                break;
            }
            else if (code == Coordination::Error::ZNONODE)
            {
                
                break;
            }
            else if (code == Coordination::Error::ZBADVERSION)
            {