fixes #282. credit @cexoso. in certain edge situations res.locals is undefined

Author: shellscape

lib/middleware.js

@@ -7,6 +7,10 @@ const { getFilenameFromUrl, handleRangeHeaders, handleRequest, ready } = require
 
 module.exports = function wrapper(context) {
   return function middleware(req, res, next) {
+    // fixes #282. credit @cexoso. in certain edge situations res.locals is
+    // undefined.
+    res.locals = res.locals || {};
+
     function goNext() {
       if (!context.options.serverSideRender) {
         return next();