Add check for IMCE

Closes #3399600

includes/html.theme

@@ -17,6 +17,11 @@ function gin_preprocess_html(&$variables) {
   $gin_activated = _gin_is_active();
 
   if ($gin_activated) {
+    // Check if IMCE is active.
+    if (isset($variables['attributes']['class']) && in_array('imce-page', $variables['attributes']['class'])) {
+      return;
+    }
+
     // Get theme settings.
     /** @var \Drupal\gin\GinSettings $settings */
     $settings = \Drupal::classResolver(GinSettings::class);