Fixing bug with Manager.hx unsafeCount() where current_row could be null.

Here's Manager.hx's code

```
    public function unsafeCount( sql : String ) {
                return unsafeExecute(sql).getIntResult(0);
        }
```

Since it doesn't call next() before executing getIntResult(0), calling `this.next()` if current_row is null fixes that problem.