**How to reproduce**
Clickhouse version 21.2-21.3

```
SELECT x
FROM
(
    SELECT 1 AS x
    UNION DISTINCT
    SELECT 1
)
LIMIT 1

Query id: b82bbb8d-dea9-4f1c-9a2f-5b0e9b6c2422


0 rows in set. Elapsed: 0.002 sec.

Received exception from server (version 21.2.3):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: Bad cast from type DB::ASTSelectWithUnionQuery to DB::ASTSelectQuery.
```


{
    auto & query = getSelectQuery();
    if (query.orderBy())
    {
        SortDescription order_descr = getSortDescription(query, *context);
        SortDescription fill_descr;
        for (auto & desc : order_descr)
        {
            if (desc.with_fill)
                fill_descr.push_back(desc);
        }
        if (fill_descr.empty())
            return;
        auto filling_step = std::make_unique<FillingStep>(query_plan.getCurrentDataStream(), std::move(fill_descr));
        query_plan.addStep(std::move(filling_step));
    }
}
void InterpreterSelectQuery::executeLimit(QueryPlan & query_plan)