version 21.5.5.12 (official build)

I'm trying to change data type for a column that is used in the TTL expression.
It works well when the table is empty.
When the table is not empty, the mutation fails.
As a result the table ends up in an inconsistent state.

```
create table test
(
InsertionDateTime DateTime,
TTLDays Int32 DEFAULT CAST(365, 'Int32')
)
Engine=MergeTree()
order by tuple()
TTL InsertionDateTime + toIntervalDay(TTLDays);

Ok.

insert into test values (now(), 23);

Ok.

ALTER TABLE test modify column TTLDays Int16 DEFAULT CAST(365, 'Int16');

Code: 341, e.displayText() = DB::Exception: Exception happened during execution of mutation 'mutation_2.txt' with part 'all_1_1_0' reason: 'Code: 10, e.displayText() = DB::Exception: Not found column InsertionDateTime in block. There are only columns: TTLDays (version 21.5.5.12 (official build))'. This error maybe retryable or not. In case of unretryable error, mutation can be killed with KILL MUTATION query (version 21.5.5.12 (official build)) [DB Errorcode=341]

insert into test values (now(), 23);

Ok.

select table, column, type, sum(rows) rows, sum(column_bytes_on_disk) on_disk
from system.parts_columns where column like 'TTLDays'
group by database, table, column, type

table | column  | type  | rows | on_disk
------+---------+-------+------+--------
test  | TTLDays | Int32 |    1 |      86
test  | TTLDays | Int16 |    1 |      84
```
LOG_DEBUG(log, "DEDUPLICATE BY all columns");
        else
            LOG_DEBUG(log, "DEDUPLICATE BY ('{}')", fmt::join(deduplicate_by_columns, "', '"));
    }
    auto disk = space_reservation->getDisk();
    String part_path = data.relative_data_path;
    String new_part_tmp_path = part_path + tmp_prefix + future_part.name + (parent_part ? ".proj" : "") + "/";
    if (disk->exists(new_part_tmp_path))
        throw Exception("Directory " + fullPath(disk, new_part_tmp_path) + " already exists", ErrorCodes::DIRECTORY_ALREADY_EXISTS);
    Names all_column_names = metadata_snapshot->getColumns().getNamesOfPhysical();
    NamesAndTypesList storage_columns = metadata_snapshot->getColumns().getAllPhysical();
    const auto data_settings = data.getSettings();
    NamesAndTypesList gathering_columns;
    NamesAndTypesList merging_columns;
    Names gathering_column_names, merging_column_names;
    extractMergingAndGatheringColumns(
        storage_columns,
        metadata_snapshot->getSortingKey().expression,
        metadata_snapshot->getSecondaryIndices(),
        metadata_snapshot->getProjections(),
        merging_params,
        gathering_columns,
        gathering_column_names,
        merging_columns,
        merging_column_names);
    auto single_disk_volume = std::make_shared<SingleDiskVolume>("volume_" + future_part.name, disk, 0);
    MergeTreeData::MutableDataPartPtr new_data_part = data.createPart(
        future_part.name,
        future_part.type,
        future_part.part_info,