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
```
if (stages.empty() || !stages.back().column_to_updated.empty())
                stages.emplace_back(context);
            if (stages.size() == 1) 
                stages.emplace_back(context);
            NameSet affected_materialized;
            for (const auto & kv : command.column_to_update_expression)
            {
                const String & column = kv.first;
                auto materialized_it = column_to_affected_materialized.find(column);
                if (materialized_it != column_to_affected_materialized.end())
                {
                    for (const String & mat_column : materialized_it->second)
                        affected_materialized.emplace(mat_column);
                }
                
                
                
                
                
                
                
                
                
                const auto & type = columns_desc.getPhysical(column).type;
                auto type_literal = std::make_shared<ASTLiteral>(type->getName());
                const auto & update_expr = kv.second;
                ASTPtr condition = getPartitionAndPredicateExpressionForMutationCommand(command);
                
                if (isArray(type) && !Nested::splitName(column).second.empty())
                {