**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)
```
{
    auto zookeeper = getZooKeeper();
    zookeeper->createAncestors(zookeeper_path);
    for (size_t i = 0; i < 1000; ++i)
    {
        
        if (zookeeper->exists(zookeeper_path + "/replicas"))
        {
            LOG_DEBUG(log, "This table {} is already created, will add new replica", zookeeper_path);
            return false;
        }
        
        if (zookeeper->exists(zookeeper_path + "/dropped"))
        {
            
            
            
            LOG_WARNING(log, "Removing leftovers from table {} (this might take several minutes)", zookeeper_path);
            Strings children;
            Coordination::Error code = zookeeper->tryGetChildren(zookeeper_path, children);
            if (code == Coordination::Error::ZNONODE)
            {
                LOG_WARNING(log, "Table {} is already finished removing by another replica right now", replica_path);
            }
            else
            {
                for (const auto & child : children)
                    if (child != "dropped")
                        zookeeper->tryRemoveRecursive(zookeeper_path + "/" + child);
                Coordination::Requests ops;