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
```
bool has_volumes_with_disabled_merges = storage_policy->hasAnyVolumeWithDisabledMerges();
    const String * prev_partition_id = nullptr;
    
    const MergeTreeData::DataPartPtr * prev_part = nullptr;
    size_t parts_selected_precondition = 0;
    for (const MergeTreeData::DataPartPtr & part : data_parts)
    {
        const String & partition_id = part->info.partition_id;
        if (!prev_partition_id || partition_id != *prev_partition_id)
        {
            if (parts_ranges.empty() || !parts_ranges.back().empty())
                parts_ranges.emplace_back();
            
            prev_partition_id = &partition_id;
            prev_part = nullptr;
        }
        
        if (!prev_part)
        {
            /* Parts can be merged with themselves for TTL needs for example.
            * So we have to check if this part is currently being inserted with quorum and so on and so forth.
            * Obviously we have to check it manually only for the first part
            * of each partition because it will be automatically checked for a pair of parts. */
            if (!can_merge_callback(nullptr, part, nullptr))
                continue;
            
            
            if (!parts_ranges.back().empty())
                parts_ranges.emplace_back();