**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)
```
const ASTPtr &,
    const StorageMetadataPtr &,
    const ASTPtr & partition,
    bool final,
    bool deduplicate,
    const Context & query_context)
{
    assertNotReadonly();
    if (!is_leader)
        throw Exception("OPTIMIZE cannot be done on this replica because it is not a leader", ErrorCodes::NOT_A_LEADER);
    constexpr size_t max_retries = 10;
    std::vector<ReplicatedMergeTreeLogEntryData> merge_entries;
    {
        auto zookeeper = getZooKeeper();
        auto handle_noop = [&] (const String & message)
        {
            if (query_context.getSettingsRef().optimize_throw_if_noop)
                throw Exception(message, ErrorCodes::CANNOT_ASSIGN_OPTIMIZE);
            return false;
        };
        const auto storage_settings_ptr = getSettings();
        if (!partition && final)
        {
            DataPartsVector data_parts = getDataPartsVector();
            std::unordered_set<String> partition_ids;
            for (const DataPartPtr & part : data_parts)