I've been studying basic usage and I found wrong minus result on DecimalXX type.

**Example Query**
`
select toDecimal64(4,4) - toDecimal32(2,2)
`

**Expected output**
2.0000

**Actual output**
3.9800

Is there anything wrong or maybe my misunderstanding of toDecimal ?

![image](https://user-images.githubusercontent.com/8475371/107513855-cdd57a00-6be3-11eb-841d-d425a198d172.png)


**How to reproduce**
1. OS: macOS Catalina 10.15.5
2. server: clickhouse-server, built from source, version 21.3.1.1
3. client:  clickhouse-client,  built from source, version 21.3.1.1

}
        else if constexpr (is_multiply)
        {
            if (scale_a != 1)
            {
                for (size_t i = 0; i < size; ++i)
                    c[i] = applyScaled<true, false>(
                        unwrap<op_case, OpCase::LeftConstant>(a, i),
                        unwrap<op_case, OpCase::RightConstant>(b, i),
                        scale_a);
                return;
            }
            else if (scale_b != 1)
            {
                for (size_t i = 0; i < size; ++i)
                    c[i] = applyScaled<false, false>(
                        unwrap<op_case, OpCase::LeftConstant>(a, i),
                        unwrap<op_case, OpCase::RightConstant>(b, i),
                        scale_b);
                return;
            }
        }
        else if constexpr (is_division && is_decimal_b)
        {
            for (size_t i = 0; i < size; ++i)
                c[i] = applyScaledDiv<is_decimal_a>(
                    unwrap<op_case, OpCase::LeftConstant>(a, i),
                    unwrap<op_case, OpCase::RightConstant>(b, i),
                    scale_a);
            return;