FIX: prevents create row to be displayed if term is in displayed list

app/assets/javascripts/select-kit/mixins/tags.js.es6

@@ -1,4 +1,4 @@
-const { run } = Ember;
+const { run, get } = Ember;
 import { ajax } from "discourse/lib/ajax";
 import { popupAjaxError } from "discourse/lib/ajax-error";
 
@@ -47,6 +47,10 @@ export default Ember.Mixin.create({
       return false;
     }
 
+    if (this.get("asyncContent").map(c => get(c, "id")).includes(term)) {
+      return false;
+    }
+
     return true;
   },
 });