**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 Names & column_names,
    const StorageMetadataPtr & metadata_snapshot,
    const SelectQueryInfo & query_info,
    const Context & context,
    QueryProcessingStage::Enum ,
    const size_t max_block_size,
    const unsigned num_streams)
{
    /** The `select_sequential_consistency` setting has two meanings:
    * 1. To throw an exception if on a replica there are not all parts which have been written down on quorum of remaining replicas.
    * 2. Do not read parts that have not yet been written to the quorum of the replicas.
    * For this you have to synchronously go to ZooKeeper.
    */
    if (context.getSettingsRef().select_sequential_consistency)
    {
        auto max_added_blocks = getMaxAddedBlocks();
        return reader.read(column_names, metadata_snapshot, query_info, context, max_block_size, num_streams, &max_added_blocks);
    }
    return reader.read(column_names, metadata_snapshot, query_info, context, max_block_size, num_streams);
}
template <class Func>
void StorageReplicatedMergeTree::foreachCommittedParts(const Func & func) const