**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)
```
else
    {
        
        return 0;
    }
}
void StorageReplicatedMergeTree::getReplicaDelays(time_t & out_absolute_delay, time_t & out_relative_delay)
{
    assertNotReadonly();
    time_t current_time = time(nullptr);
    out_absolute_delay = getAbsoluteDelay();
    out_relative_delay = 0;
    const auto storage_settings_ptr = getSettings();
    /** Relative delay is the maximum difference of absolute delay from any other replica,
      *  (if this replica lags behind any other live replica, or zero, otherwise).
      * Calculated only if the absolute delay is large enough.
      */
    if (out_absolute_delay < static_cast<time_t>(storage_settings_ptr->min_relative_delay_to_measure))
        return;
    auto zookeeper = getZooKeeper();
    time_t max_replicas_unprocessed_insert_time = 0;
    bool have_replica_with_nothing_unprocessed = false;
    Strings replicas = zookeeper->getChildren(zookeeper_path + "/replicas");
    for (const auto & replica : replicas)
    {
        if (replica == replica_name)
            continue;
        
        if (!zookeeper->exists(zookeeper_path + "/replicas/" + replica + "/is_active"))
            continue;