Additional bug fix to range picker when next date is before previous date

This PR contains some additional to outstanding PR #937

Steps to reproduce:

http://eternicode.github.io/bootstrap-datepicker

1. Select range picker.
1. In second input select some date.
1. In first input select the date after the second date.

Expected: The second date will not immediately change to be the same as first.

Actual: You have to change first one again to something in future and then it works fine.