[Scrutinizer] Fix undeclared variables in src/ (except Protocol/)

- Use dba::selectFirst to remove intermediate variables `$r`
- Remove unused variable `$url_recipients` in Worker\Dellivery

src/Core/Cache.php

@@ -76,6 +76,7 @@ class Cache
 				$seconds = 300;
 				break;
 			case CACHE_MINUTE:
+			default:
 				$seconds = 60;
 				break;
 		}