**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 (future_merged_part.name != entry.new_part_name)
    {
        throw Exception("Future merged part name " + backQuote(future_merged_part.name) + " differs from part name in log entry: "
            + backQuote(entry.new_part_name), ErrorCodes::BAD_DATA_PART_NAME);
    }
    future_merged_part.updatePath(*this, reserved_space);
    future_merged_part.merge_type = entry.merge_type;
    auto table_id = getStorageID();
    MergeList::EntryPtr merge_entry = global_context.getMergeList().insert(table_id.database_name, table_id.table_name, future_merged_part);
    Transaction transaction(*this);
    MutableDataPartPtr part;
    Stopwatch stopwatch;
    auto write_part_log = [&] (const ExecutionStatus & execution_status)
    {
        writePartLog(
            PartLogElement::MERGE_PARTS, execution_status, stopwatch.elapsed(),
            entry.new_part_name, part, parts, merge_entry.get());
    };
    try
    {
        part = merger_mutator.mergePartsToTemporaryPart(
            future_merged_part, metadata_snapshot, *merge_entry,
            table_lock, entry.create_time, global_context, reserved_space, entry.deduplicate);
        merger_mutator.renameMergedTemporaryPart(part, parts, &transaction);
        try
        {
            checkPartChecksumsAndCommit(transaction, part);
        }
        catch (const Exception & e)
        {