Checking if late_flag is 0 before defaulting it

Refer to: http://manage.dimagi.com/default.asp?142358#797925
this would arguably be a more accurate reflection of the intent if it read:
```javascript
this.original.late_flag = this.original.late_flag !== null ? this.original.late_flag : 30;
```

(though i don't know if the overhead of making sure it's not ever, e.g. `undefined` or an empty string is worth it.