**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)
```
if (!old_added_parts.empty())
            parts_with_quorum.fromString(old_added_parts);
        
        if (!parts_with_quorum.added_parts.count(partition_id))
        {
            
            break;
        }
        parts_with_quorum.added_parts.erase(partition_id);
        String new_added_parts = parts_with_quorum.toString();
        auto code = zookeeper->trySet(quorum_last_part_path, new_added_parts, added_parts_stat.version);
        if (code == Coordination::Error::ZOK)
        {
            break;
        }
        else if (code == Coordination::Error::ZNONODE)
        {
            
            break;
        }
        else if (code == Coordination::Error::ZBADVERSION)
        {
            
            continue;
        }
        else
            throw Coordination::Exception(code, quorum_last_part_path);
    }
}
bool StorageReplicatedMergeTree::fetchPart(const String & part_name, const StorageMetadataPtr & metadata_snapshot,