**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 (log_entries.empty())
            {
                res.log_max_index = 0;
            }
            else
            {
                const String & last_log_entry = *std::max_element(log_entries.begin(), log_entries.end());
                res.log_max_index = parse<UInt64>(last_log_entry.substr(strlen("log-")));
            }
            String log_pointer_str = zookeeper->get(replica_path + "/log_pointer");
            res.log_pointer = log_pointer_str.empty() ? 0 : parse<UInt64>(log_pointer_str);
            auto all_replicas = zookeeper->getChildren(zookeeper_path + "/replicas");
            res.total_replicas = all_replicas.size();
            res.active_replicas = 0;
            for (const String & replica : all_replicas)
                if (zookeeper->exists(zookeeper_path + "/replicas/" + replica + "/is_active"))
                    ++res.active_replicas;
        }
        catch (const Coordination::Exception &)
        {
            res.zookeeper_exception = getCurrentExceptionMessage(false);
        }
    }
}
void StorageReplicatedMergeTree::getQueue(LogEntriesData & res, String & replica_name_)
{
    replica_name_ = replica_name;
    queue.getEntries(res);
}
time_t StorageReplicatedMergeTree::getAbsoluteDelay() const