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
```
FutureMergedMutatedPart projection_future_part;
                MergeTreeData::DataPartsVector const_selected_parts(
                    std::make_move_iterator(selected_parts.begin()), std::make_move_iterator(selected_parts.end()));
                projection_future_part.assign(std::move(const_selected_parts));
                projection_future_part.name = fmt::format("{}_{}", projection.name, ++block_num);
                projection_future_part.part_info = {"all", 0, 0, 0};
                MergeTreeData::MergingParams projection_merging_params;
                projection_merging_params.mode = MergeTreeData::MergingParams::Ordinary;
                if (projection.type == ProjectionDescription::Type::Aggregate)
                    projection_merging_params.mode = MergeTreeData::MergingParams::Aggregating;
                LOG_DEBUG(log, "Merged {} parts in level {} to {}", selected_parts.size(), current_level, projection_future_part.name);
                next_level_parts.push_back(mergePartsToTemporaryPart(
                    projection_future_part,
                    projection.metadata,
                    merge_entry,
                    holder,
                    time_of_mutation,
                    context,
                    space_reservation,
                    false, 
                    {},
                    projection_merging_params,
                    new_data_part.get(),
                    "tmp_merge_"));
                next_level_parts.back()->is_temp = true;
            }
        }
    }
}
void MergeTreeDataMergerMutator::mutateAllPartColumns(