FIX: Update preview when autocomplete is clicked (#10430)

app/assets/javascripts/discourse/app/components/composer-editor.js

@@ -188,7 +188,9 @@ export default Component.extend({
         dataSource: term => this.userSearchTerm.call(this, term),
         key: "@",
         transformComplete: v => v.username || v.name,
-        afterComplete() {
+        afterComplete: value => {
+          this.composer.set("reply", value);
+
           // ensures textarea scroll position is correct
           schedule("afterRender", () => $input.blur().focus());
         },