Updating a Nullable column value by using alter .... where ... causes to set another value!

ClickHouse version: 20.6.3.28
Engine: MergeTree
OS: Ubuntu 18.04.3 LTS

Steps to reproduce:
```sql
CREATE TABLE table1(
	id int,
	price Nullable(Int32)
)
ENGINE = MergeTree()
PARTITION BY id
ORDER BY (id);
INSERT INTO table1 (id, price) VALUES (1, 100);
ALTER TABLE table1  update price = 150 where id=1;
SELECT * FROM table1;
```
We expect the price to be `150`, but it's `93148480`:

```
┌─id─┬────price─┐
│  1 │ 93148480 │
└────┴──────────┘
```
Using `Decimal(9,2)` field instead of `Int32` would set the value  `932342.88` always. It seems there's a fixed value for each data type.

If we don't use such a `where` clause, it works correctly:
```sql
ALTER TABLE db1.table1  update price = 150 where 1=1;
┌─id─┬─price─┐
│  1 │   150 │
└────┴───────┘
```
if (isColumnNullable(*arg_then.column))
                {
                    auto arg_then_column = arg_then.column;
                    auto result_column = IColumn::mutate(std::move(arg_then_column));
                    assert_cast<ColumnNullable &>(*result_column).applyNegatedNullMap(assert_cast<const ColumnUInt8 &>(*arg_cond.column));
                    block.getByPosition(result).column = std::move(result_column);
                }
                else
                {
                    block.getByPosition(result).column = ColumnNullable::create(
                        materializeColumnIfConst(arg_then.column), std::move(negated_null_map));
                }
            }
            else if (cond_const_col)
            {
                if (cond_const_col->getValue<UInt8>())
                    block.getByPosition(result).column = makeNullableColumnIfNot(arg_then.column);
                else
                    block.getByPosition(result).column = block.getByPosition(result).type->createColumn()->cloneResized(input_rows_count);
            }
            else
                throw Exception("Illegal column " + arg_cond.column->getName() + " of first argument of function " + getName()
                    + ". Must be ColumnUInt8 or ColumnConstUInt8.",
                    ErrorCodes::ILLEGAL_COLUMN);
            return true;
        }
        return false;
    }
public:
    String getName() const override