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 │
└────┴───────┘
```
bool isFixedAndContiguous() const override { return true; }
    size_t sizeOfValueIfFixed() const override { return sizeof(T); }
    StringRef getRawData() const override
    {
        return StringRef(reinterpret_cast<const char*>(data.data()), byteSize());
    }
    StringRef getDataAt(size_t n) const override
    {
        return StringRef(reinterpret_cast<const char *>(&data[n]), sizeof(data[n]));
    }
    bool structureEquals(const IColumn & rhs) const override
    {
        return typeid(rhs) == typeid(ColumnVector<T>);
    }
    
    void applyZeroMap(const IColumn::Filter & filt, bool inverted = false);
    
    Container & getData()
    {
        return data;
    }
    const Container & getData() const
    {
        return data;
    }
    const T & getElement(size_t n) const