Allow the URL helper to be created even if Application does not yet have MvcEvent. (#5063)

While this shouldn't happen, anything (such as an event listener) that tries to create the plugin before MvcEvent is created for Application would cause an error.

Author: EreMaijala

module/VuFind/src/VuFind/View/Helper/Root/UrlFactory.php

@@ -79,7 +79,7 @@ public function __invoke(
 
         $match = $container->get('Application')
             ->getMvcEvent()
-            ->getRouteMatch();
+            ?->getRouteMatch();
 
         if ($match instanceof RouteMatch) {
             $helper->setRouteMatch($match);