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
```
} 
    {
        auto out = disk->writeFile(new_data_part->getFullRelativePath() + IMergeTreeDataPart::DEFAULT_COMPRESSION_CODEC_FILE_NAME, 4096);
        DB::writeText(queryToString(codec->getFullCodecDesc()), *out);
    }
    {
        
        auto out_columns = disk->writeFile(fs::path(new_data_part->getFullRelativePath()) / "columns.txt", 4096);
        new_data_part->getColumns().writeText(*out_columns);
    } 
    new_data_part->rows_count = source_part->rows_count;
    new_data_part->index_granularity = source_part->index_granularity;
    new_data_part->index = source_part->index;
    new_data_part->minmax_idx = source_part->minmax_idx;
    new_data_part->modification_time = time(nullptr);
    new_data_part->loadProjections(false, false);
    new_data_part->setBytesOnDisk(
        MergeTreeData::DataPart::calculateTotalSizeOnDisk(new_data_part->volume->getDisk(), new_data_part->getFullRelativePath()));
    new_data_part->default_codec = codec;
    new_data_part->calculateColumnsSizesOnDisk();
    new_data_part->storage.lockSharedData(*new_data_part);
}
bool MergeTreeDataMergerMutator::checkOperationIsNotCanceled(const MergeListEntry & merge_entry) const
{
    if (merges_blocker.isCancelled() || merge_entry->is_cancelled)
        throw Exception("Cancelled mutating parts", ErrorCodes::ABORTED);
    return true;
}
}