Fix validation issue
Fix validation issue

* When a min/max date value is provided to the input that isn't a valid
moment, the validation will mark any dates as valid.

DanTalash/angular-datepicker,g00fy-/angular-datepicker,frontapp/angular-datepicker,g00fy-/angular-datepicker,DanTalash/angular-datepicker,pankas87/angular-datepicker-dirty-fix,pankas87/angular-datepicker-dirty-fix,frontapp/angular-datepicker