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
```
rename_vector.emplace_back(stream_from + ".bin", stream_to + ".bin");
                    rename_vector.emplace_back(stream_from + mrk_extension, stream_to + mrk_extension);
                }
            };
            auto column = source_part->getColumns().tryGetByName(command.column_name);
            if (column)
            {
                auto serialization = source_part->getSerializationForColumn(*column);
                serialization->enumerateStreams(callback);
            }
        }
    }
    return rename_vector;
}
NameSet MergeTreeDataMergerMutator::collectFilesToSkip(
    const MergeTreeDataPartPtr & source_part,
    const Block & updated_header,
    const std::set<MergeTreeIndexPtr> & indices_to_recalc,
    const String & mrk_extension,
    const std::set<MergeTreeProjectionPtr> & projections_to_recalc)
{
    NameSet files_to_skip = source_part->getFileNamesWithoutChecksums();
    
    for (const auto & entry : updated_header)
    {
        ISerialization::StreamCallback callback = [&](const ISerialization::SubstreamPath & substream_path)
        {
            String stream_name = ISerialization::getFileNameForStream({entry.name, entry.type}, substream_path);
            files_to_skip.insert(stream_name + ".bin");
            files_to_skip.insert(stream_name + mrk_extension);