FIX: Close navigation dropdown when item selected (#12155)

This `if` statement was backwards, such that it was a no-op. This hasn't
caused a problem because clicking an item triggers a page load, which
destroys and recreates the component.

However, we are soon planning to remove the intermediate loading screen,
which means the component will not be removed/recreated.

https://meta.discourse.org/t/177939/202

app/assets/javascripts/discourse/app/components/navigation-bar.js

@@ -52,7 +52,7 @@ export default Component.extend(FilterModeMixin, {
   },
 
   ensureDropClosed() {
-    if (!this.expanded) {
+    if (this.expanded) {
       this.set("expanded", false);
     }
     $(window).off("click.navigation-bar");