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 if (command.type == MutationCommand::Type::DROP_COLUMN)
        {
            ISerialization::StreamCallback callback = [&](const ISerialization::SubstreamPath & substream_path)
            {
                String stream_name = ISerialization::getFileNameForStream({command.column_name, command.data_type}, substream_path);
                
                if (--stream_counts[stream_name] == 0)
                {
                    rename_vector.emplace_back(stream_name + ".bin", "");
                    rename_vector.emplace_back(stream_name + mrk_extension, "");
                }
            };
            auto column = source_part->getColumns().tryGetByName(command.column_name);
            if (column)
            {
                auto serialization = source_part->getSerializationForColumn(*column);
                serialization->enumerateStreams(callback);
            }
        }
        else if (command.type == MutationCommand::Type::RENAME_COLUMN)
        {
            String escaped_name_from = escapeForFileName(command.column_name);
            String escaped_name_to = escapeForFileName(command.rename_to);
            ISerialization::StreamCallback callback = [&](const ISerialization::SubstreamPath & substream_path)
            {
                String stream_from = ISerialization::getFileNameForStream({command.column_name, command.data_type}, substream_path);
                String stream_to = boost::replace_first_copy(stream_from, escaped_name_from, escaped_name_to);
                if (stream_from != stream_to)
                {