Make cover router factory more error-tolerant.

- Allows the cover router to operate in more contexts (CLI vs. web)

module/VuFind/src/VuFind/Cover/RouterFactory.php

@@ -61,8 +61,15 @@ class RouterFactory implements FactoryInterface
         if (!empty($options)) {
             throw new \Exception('Unexpected options sent to factory.');
         }
-        $base = $container->get('ControllerPluginManager')->get('url')
-            ->fromRoute('cover-show');
+        // Try to get the base URL from the controller plugin; fail over to
+        // the view helper if that doesn't work.
+        try {
+            $base = $container->get('ControllerPluginManager')->get('url')
+                ->fromRoute('cover-show');
+        } catch (\Exception $e) {
+            $base = $container->get('ViewRenderer')->plugin('url')
+                ->__invoke('cover-show');
+        }
         return new $requestedName($base);
     }
 }