Issue #3439285: dont throw a NotFoundHttpException if main domain isnt configured

Closes #3439285

src/EventSubscriber/PathRequestSubscriber.php

@@ -92,6 +92,12 @@ final class PathRequestSubscriber implements EventSubscriberInterface {
 
     $request = $event->getRequest();
 
+    // If main domain isn't configured don't run the risk of inaccessible
+    // groups.
+    if (empty($this->mainDomain)) {
+      return;
+    }
+
     // Don't act on the main domain as well, all should be accessible there.
     if ($this->mainDomain !== NULL && $request->getHttpHost() === $this->mainDomain) {
       return;