**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 (partial_shutdown_called)
            throw Exception("Mutation is not finished because table shutdown was called. It will be done after table restart.",
                ErrorCodes::UNFINISHED);
    }
    if (!inactive_replicas.empty())
    {
        std::stringstream exception_message;
        exception_message << "Mutation is not finished because";
        if (!inactive_replicas.empty())
            exception_message << " some replicas are inactive right now: " << boost::algorithm::join(inactive_replicas, ", ");
        exception_message << ". Mutation will be done asynchronously";
        throw Exception(exception_message.str(), ErrorCodes::UNFINISHED);
    }
}
void StorageReplicatedMergeTree::createNewZooKeeperNodes()
{
    auto zookeeper = getZooKeeper();
    
    zookeeper->createIfNotExists(zookeeper_path + "/quorum", String());
    zookeeper->createIfNotExists(zookeeper_path + "/quorum/parallel", String());
    zookeeper->createIfNotExists(zookeeper_path + "/quorum/last_part", String());
    zookeeper->createIfNotExists(zookeeper_path + "/quorum/failed_parts", String());
    
    zookeeper->createIfNotExists(replica_path + "/min_unprocessed_insert_time", String());
    zookeeper->createIfNotExists(replica_path + "/max_processed_insert_time", String());
    
    zookeeper->createIfNotExists(zookeeper_path + "/mutations", String());
    zookeeper->createIfNotExists(replica_path + "/mutation_pointer", String());
}
bool StorageReplicatedMergeTree::createTableIfNotExists(const StorageMetadataPtr & metadata_snapshot)