Fix console error caused by missing mount element

"Allow access to the following IP addresses" and
"Restrict membership by email domain" fields are only shown on the
root group. This was causing console errors on the subgroups because
the mount element was missing.

ee/app/assets/javascripts/groups/settings/access_restriction_field/index.js

@@ -2,7 +2,11 @@ import Vue from 'vue';
 import { __, sprintf } from '~/locale';
 import CommaSeparatedListTokenSelector from '../components/comma_separated_list_token_selector.vue';
 
-export default (el, props = {}, qaSelector, customValidator) => {
+export default (selector, props = {}, qaSelector, customValidator) => {
+  const el = document.querySelector(selector);
+
+  if (!el) return;
+
   // eslint-disable-next-line no-new
   new Vue({
     el,
@@ -10,9 +14,7 @@ export default (el, props = {}, qaSelector, customValidator) => {
       CommaSeparatedListTokenSelector,
     },
     data() {
-      const { hiddenInputId, labelId, regexValidator, disallowedValues } = document.querySelector(
-        this.$options.el,
-      ).dataset;
+      const { hiddenInputId, labelId, regexValidator, disallowedValues } = el.dataset;
 
       return {
         hiddenInputId,