#3426896 Check for active theme befor altering the form.

Closes #3426896

gin_everywhere.module

@@ -43,6 +43,15 @@ function gin_everywhere_form_alter(&$form, FormStateInterface $form_state, $form
   if (!$form_state->getFormObject() instanceof ContentEntityFormInterface) {
     return;
   }
+
+  // Don't transform the form if we are not on the gin theme. This may happen if
+  // we are acting in a frontend form like layout_builder.
+  $active_theme = \Drupal::theme()->getActiveTheme();
+  $base_themes = (array) $active_theme->getBaseThemeExtensions();
+  if (!($active_theme->getName() === 'gin' || array_key_exists('gin', $base_themes))) {
+    return;
+  }
+
   if (!isset($form['advanced'])) {
     $form['advanced'] = [
       '#type' => 'vertical_tabs',