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
```
MergeListEntry & merge_entry,
        bool need_remove_expired_values,
        bool need_sync,
        const ReservationPtr & space_reservation,
        TableLockHolder & holder,
        ContextPtr context);
    
    void mutateSomePartColumns(
        const MergeTreeDataPartPtr & source_part,
        const StorageMetadataPtr & metadata_snapshot,
        const std::set<MergeTreeIndexPtr> & indices_to_recalc,
        const std::set<MergeTreeProjectionPtr> & projections_to_recalc,
        const Block & mutation_header,
        MergeTreeData::MutableDataPartPtr new_data_part,
        BlockInputStreamPtr mutating_stream,
        time_t time_of_mutation,
        const CompressionCodecPtr & compression_codec,
        MergeListEntry & merge_entry,
        bool need_remove_expired_values,
        bool need_sync,
        const ReservationPtr & space_reservation,
        TableLockHolder & holder,
        ContextPtr context);
    
    
    static void finalizeMutatedPart(
        const MergeTreeDataPartPtr & source_part,
        MergeTreeData::MutableDataPartPtr new_data_part,
        bool need_remove_expired_values,
        const CompressionCodecPtr & codec);