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
```
mutation_kind == MutationsInterpreter::MutationKind::MUTATE_INDEX_PROJECTION ? Block{} : updated_header,
                new_data_part,
                in,
                time_of_mutation,
                compression_codec,
                merge_entry,
                need_remove_expired_values,
                need_sync,
                space_reservation,
                holder,
                context);
        }
        for (const auto & [rename_from, rename_to] : files_to_rename)
        {
            if (rename_to.empty() && new_data_part->checksums.files.count(rename_from))
            {
                new_data_part->checksums.files.erase(rename_from);
            }
            else if (new_data_part->checksums.files.count(rename_from))
            {
                new_data_part->checksums.files[rename_to] = new_data_part->checksums.files[rename_from];
                new_data_part->checksums.files.erase(rename_from);
            }
        }
        finalizeMutatedPart(source_part, new_data_part, need_remove_expired_values, compression_codec);
    }
    return new_data_part;
}
MergeAlgorithm MergeTreeDataMergerMutator::chooseMergeAlgorithm(