Always fire notify fix

This would fix a state where `notify()` fires only if the range is present. If there is no range present ( same day selected ) or `cancel` has been clicked no notification would be send.

``` js
$('input[name="daterange"]').daterangepicker({ format: 'YYYY-MM-DD', startDate: '2013-01-01', endDate: '2013-12-31' }, function notify(start, end) { 
   console.log('A date range was chosen: ' + start.format('YYYY-MM-DD') + ' to ' + end.format('YYYY-MM-DD'));
});
```