Try to prevent late/duplicate response errors (#20077)

* Ensure all Express 'next' calls include 'return's

* Add headersSent checks during archived versions flow

* Return a 404 earlier if archived resource fetch fails

* Short-circuit responses for archived stuff

* Be more careful about responding to and short-circuiting after search requests

* Fix tests

middleware/is-next-request.js

@@ -1,11 +1,11 @@
-const { FEATURE_NEXTJS } = process.env;
+const { FEATURE_NEXTJS } = process.env
 
-module.exports = function isNextRequest(req, res, next) {
-  req.renderWithNextjs = false;
+module.exports = function isNextRequest (req, res, next) {
+  req.renderWithNextjs = false
 
   if (FEATURE_NEXTJS) {
-    req.renderWithNextjs = true;
+    req.renderWithNextjs = true
   }
 
-  next();
-};
+  return next()
+}