class ng-touched not set if using AltInput

[david-dasilva]

Describe the bug
Hi,

I found an issue where some Angular's classes for form are not set up correctly on some cases :
If using AltInput, the ng-touched is not set on the datepicker when clicking, and even selecting a date.

Expected behavior
When I click on the datepicker, the css class ng-touched is set on the element, and the class ng-untouched should disapear.

Reproduction
Here is a Stackblitz to showcase it : https://stackblitz.com/edit/ng2-flatpickr-issue-starter-duia6u
and a github : https://github.com/david-dasilva/ng-flatpicker-issue

Clicking on the first datepicker and closing it does not remove the ng-untouched class and does not set the ng-touched class.

On the second datepicker, it works as intended.

Desktop (please complete the following information):

• OS: Ubuntu 18.04
• Browser Firefox 72 / Chromium 79