Add context to Response for including file and file_not_found to be identified by other shelf Middleware.

pkgs/shelf_static/lib/src/static_handler.dart

@@ -198,7 +198,8 @@ Handler createFileHandler(String path, {String? url, String? contentType}) {
 
   return (request) {
     if (request.url.path != url) {
-      var fileNotFound = File(p.join(parent.path, request.url.path));
+      var fileNotFound =
+          File(p.joinAll([parent.path, ...p.split(request.url.path)]));
       return Response.notFound(
         'Not Found',
         context: buildResponseContext(fileNotFound: fileNotFound),