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
```
for (size_t i = 0, size = projections_to_build.size(); i < size; ++i)
        {
            const auto & projection = projections_to_build[i]->projection;
            auto in = InterpreterSelectQuery(
                          projection.query_ast,
                          context,
                          Pipe(std::make_shared<SourceFromSingleChunk>(block, Chunk(block.getColumns(), block.rows()))),
                          SelectQueryOptions{
                              projection.type == ProjectionDescription::Type::Normal ? QueryProcessingStage::FetchColumns : QueryProcessingStage::WithMergeableState})
                          .execute()
                          .getInputStream();
            in = std::make_shared<SquashingBlockInputStream>(in, block.rows(), std::numeric_limits<UInt64>::max());
            in->readPrefix();
            auto & projection_squash = projection_squashes[i];
            auto projection_block = projection_squash.add(in->read());
            if (in->read())
                throw Exception("Projection cannot increase the number of rows in a block", ErrorCodes::LOGICAL_ERROR);
            in->readSuffix();
            if (projection_block)
            {
                projection_parts[projection.name].emplace_back(
                    MergeTreeDataWriter::writeTempProjectionPart(data, log, projection_block, projection, new_data_part.get(), ++block_num));
            }
        }
        merge_entry->rows_written += block.rows();
        merge_entry->bytes_written_uncompressed += block.bytes();
    }
    
    for (size_t i = 0, size = projections_to_build.size(); i < size; ++i)
    {