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 │
└────┴───────┘
```
const ColumnWithTypeAndName & arg_else = block.getByPosition(arguments[2]);
        
        if (arg_then.column.get() == arg_else.column.get())
        {
            
            block.getByPosition(result).column = arg_then.column;
            return;
        }
        const ColumnUInt8 * cond_col = typeid_cast<const ColumnUInt8 *>(arg_cond.column.get());
        const ColumnConst * cond_const_col = checkAndGetColumnConst<ColumnVector<UInt8>>(arg_cond.column.get());
        ColumnPtr materialized_cond_col;
        if (cond_const_col)
        {
            if (arg_then.type->equals(*arg_else.type))
            {
                block.getByPosition(result).column = cond_const_col->getValue<UInt8>()
                    ? arg_then.column
                    : arg_else.column;
                return;
            }
            else
            {
                materialized_cond_col = cond_const_col->convertToFullColumn();
                cond_col = typeid_cast<const ColumnUInt8 *>(&*materialized_cond_col);
            }
        }
        if (!cond_col)
            throw Exception("Illegal column " + arg_cond.column->getName() + " of first argument of function " + getName()
                + ". Must be ColumnUInt8 or ColumnConstUInt8.",
                ErrorCodes::ILLEGAL_COLUMN);