**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)
```
ErrorCodes::CANNOT_ASSIGN_ALTER);
            continue;
        }
        else
        {
            throw Coordination::Exception("Alter cannot be assigned because of Zookeeper error", rc);
        }
    }
    table_lock_holder.reset();
    std::vector<String> unwaited;
    if (query_context.getSettingsRef().replication_alter_partitions_sync == 2)
    {
        LOG_DEBUG(log, "Updated shared metadata nodes in ZooKeeper. Waiting for replicas to apply changes.");
        unwaited = waitForAllReplicasToProcessLogEntry(*alter_entry, false);
    }
    else if (query_context.getSettingsRef().replication_alter_partitions_sync == 1)
    {
        LOG_DEBUG(log, "Updated shared metadata nodes in ZooKeeper. Waiting for replicas to apply changes.");
        waitForReplicaToProcessLogEntry(replica_name, *alter_entry);
    }
    if (!unwaited.empty())
        throw Exception("Some replicas doesn't finish metadata alter", ErrorCodes::UNFINISHED);
    if (mutation_znode)
    {
        LOG_DEBUG(log, "Metadata changes applied. Will wait for data changes.");
        waitMutation(*mutation_znode, query_context.getSettingsRef().replication_alter_partitions_sync);
        LOG_DEBUG(log, "Data changes applied.");
    }
}
Pipe StorageReplicatedMergeTree::alterPartition(