Resolve #3452393 "Disable username changes"

Closes #3452393

simple_account_policy.module

@@ -103,6 +103,11 @@ function simple_account_policy_form_user_form_alter(&$form, FormStateInterface $
   /** @var \Drupal\simple_account_policy\AccountPolicyInterface $accountPolicy */
   $accountPolicy = \Drupal::service('simple_account_policy');
 
+  $user_prevent_changes = ($accountPolicy->getConfiguration()->get('username_prevent_changes') ?? FALSE);
+  if ($accountPolicy->applyPolicy($currentUser) && $user_prevent_changes) {
+    $form['account']['name']['#disabled'] = TRUE;
+  }
+
   // We need user input here, since fields are not in values (yet).
   $input = $form_state->getUserInput();
   $data = [
@@ -112,10 +117,6 @@ function simple_account_policy_form_user_form_alter(&$form, FormStateInterface $
   $errors = empty($pass) ? [] : $accountPolicy->validate($currentUser, $data);
   $policy = $accountPolicy->policy($currentUser, $errors);
 
-  if ($accountPolicy->getConfiguration()->get('username_prevent_changes') ?? FALSE) {
-    $form['account']['name']['#disabled'] = TRUE;
-  }
-
   if (!empty($policy['mail'])) {
     $form['account']['mail']['#description'] = $policy['mail'];
   }