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
```
throw Exception("ALTER UPDATE/DELETE ... IN PARTITION is not supported for non-MergeTree tables", ErrorCodes::NOT_IMPLEMENTED);
        if (command.partition && storage_from_merge_tree_data_part)
        {
            const String partition_id = storage_from_merge_tree_data_part->getPartitionIDFromQuery(command.partition, context_copy);
            if (partition_id == storage_from_merge_tree_data_part->getPartitionId())
                all_commands_can_be_skipped = false;
        }
        else
            all_commands_can_be_skipped = false;
    }
    if (all_commands_can_be_skipped)
        return false;
    context_copy->setSetting("max_streams_to_max_threads_ratio", 1);
    context_copy->setSetting("max_threads", 1);
    ASTPtr select_query = prepareQueryAffectedAST(commands, storage, context_copy);
    
    
    
    InterpreterSelectQuery interpreter(select_query, context_copy, storage, metadata_snapshot, SelectQueryOptions().ignoreLimits());
    BlockInputStreamPtr in = interpreter.execute().getInputStream();
    Block block = in->read();
    if (!block.rows())
        return false;
    else if (block.rows() != 1)
        throw Exception("count() expression returned " + toString(block.rows()) + " rows, not 1",
            ErrorCodes::LOGICAL_ERROR);
    auto count = (*block.getByName("count()").column)[0].get<UInt64>();
    return count != 0;
}
ASTPtr getPartitionAndPredicateExpressionForMutationCommand(