**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
            {
                auto tuple = makeASTFunction("tuple");
                tuple->arguments->children = new_sorting_key_expr_list->children;
                order_by_ast = tuple;
            }
            return order_by_ast;
        };
        if (metadata_diff.sorting_key_changed)
        {
            auto order_by_ast = parse_key_expr(metadata_diff.new_sorting_key);
            auto & sorting_key = new_metadata.sorting_key;
            auto & primary_key = new_metadata.primary_key;
            sorting_key.recalculateWithNewAST(order_by_ast, new_metadata.columns, global_context);
            if (primary_key.definition_ast == nullptr)
            {
                
                
                auto old_sorting_key_ast = old_metadata.getSortingKey().definition_ast;
                primary_key = KeyDescription::getKeyFromAST(
                    old_sorting_key_ast, new_metadata.columns, global_context);
            }
        }
        if (metadata_diff.sampling_expression_changed)
        {
            auto sample_by_ast = parse_key_expr(metadata_diff.new_sampling_expression);
            new_metadata.sampling_key.recalculateWithNewAST(sample_by_ast, new_metadata.columns, global_context);
        }
        if (metadata_diff.skip_indices_changed)
            new_metadata.secondary_indices = IndicesDescription::parse(metadata_diff.new_skip_indices, new_columns, global_context);