TiDB returns error instead of warning for some truncated error

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
SELECT FOUND_ROWS() - 3;
```

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

```

mysql> SELECT FOUND_ROWS() - 3;
+------------------+
| FOUND_ROWS() - 3 |
+------------------+
| -2 |
+------------------+
1 row in set, 1 warning (0.02 sec)
```

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

```
mysql> SELECT FOUND_ROWS() - 3;
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(found_rows() - 3)'
```

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