some json functions have compatibility issue with MySQL

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
select json_valid(_binary'[1]');
select json_extract(_binary'{"a":1}', '$.a');
```

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

report an error

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

no error and `json_valid` return 1

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