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
```
plan.addStep(std::make_unique<FilterStep>(plan.getCurrentDataStream(), step->actions(), stage.filter_column_names[i], false));
            }
            else
            {
                
                plan.addStep(std::make_unique<ExpressionStep>(plan.getCurrentDataStream(), step->actions()));
            }
        }
        SubqueriesForSets & subqueries_for_sets = stage.analyzer->getSubqueriesForSets();
        if (!subqueries_for_sets.empty())
        {
            const Settings & settings = context->getSettingsRef();
            SizeLimits network_transfer_limits(
                    settings.max_rows_to_transfer, settings.max_bytes_to_transfer, settings.transfer_overflow_mode);
            addCreatingSetsStep(plan, std::move(subqueries_for_sets), network_transfer_limits, context);
        }
    }
    QueryPlanOptimizationSettings do_not_optimize_plan;
    do_not_optimize_plan.optimize_plan = false;
    auto pipeline = plan.buildQueryPipeline(
        do_not_optimize_plan,
        BuildQueryPipelineSettings::fromContext(context));
    pipeline->addSimpleTransform([&](const Block & header)
    {
        return std::make_shared<MaterializingTransform>(header);
    });
    return pipeline;
}
void MutationsInterpreter::validate()