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
```
}
            else
            {
                destination += it->name();
            }
            if (!disk->isDirectory(it->path()))
                disk->createHardLink(it->path(), destination);
            else if (!startsWith("tmp_", it->name())) 
            {
                
                disk->createDirectories(destination);
                for (auto p_it = disk->iterateDirectory(it->path()); p_it->isValid(); p_it->next())
                {
                    String p_destination = destination + "/";
                    String p_file_name = p_it->name();
                    p_destination += p_it->name();
                    disk->createHardLink(p_it->path(), p_destination);
                }
            }
        }
        merge_entry->columns_written = storage_columns.size() - updated_header.columns();
        new_data_part->checksums = source_part->checksums;
        auto compression_codec = source_part->default_codec;
        if (in)
        {
            mutateSomePartColumns(
                source_part,
                metadata_snapshot,
                indices_to_recalc,
                projections_to_recalc,