fix(pat-date-picker): Do not throw a blur event after selecting a date.

When a date was selected with the date picker a `blur` and `changed`
event was thrown. Now we only throw a `changed` event if da date was
selected. If no date was selected we throw a `blur` event allow
pat-validation do validate required date input fields when no value was
given.

Author: thet

src/pat/date-picker/date-picker.js

@@ -168,7 +168,7 @@ export default Base.extend({
             showWeekNumber: this.options.weekNumbers === "show",
             onSelect: () => this.dispatch_change_event(),
             onClose: () => {
-                if (this.options.behavior === "styled") {
+                if (this.options.behavior === "styled" && !this.el.value) {
                     // blur the input field so that pat-validate can kick in when
                     // nothing was selected.
                     el.dispatchEvent(events.blur_event());