The `DATE_FORMAT` is not compatible with MySQL for 0 date

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

### 2. What did you expect to see? (Required)

```
mysql> SELECT DATE_FORMAT(0, '%Y%m%d');
+--------------------------+
| DATE_FORMAT(0, '%Y%m%d') |
+--------------------------+
| 00000000 |
+--------------------------+
1 row in set (0.02 sec)
```

### 3. What did you see instead (Required)

```
mysql> SELECT DATE_FORMAT(0, '%Y%m%d');
+--------------------------+
| DATE_FORMAT(0, '%Y%m%d') |
+--------------------------+
| NULL |
+--------------------------+
1 row in set (0.00 sec)
```

### 4. What is your TiDB version? (Required)