[fix] be defensive and ensure location is in headers before running url.parse()

Author: jcrugzz

lib/http-proxy/passes/web-outgoing.js

@@ -47,7 +47,9 @@ var redirectRegex = /^30(1|2|7|8)$/;
   },
 
   function setRedirectHostRewrite(req, res, proxyRes, options) {
-    if (options.hostRewrite && redirectRegex.test(proxyRes.statusCode)) {
+    if (options.hostRewrite
+        && proxyRes.headers['location']
+        && redirectRegex.test(proxyRes.statusCode)) {
       var u = url.parse(proxyRes.headers['location']);
       u.host = options.hostRewrite;
       proxyRes.headers['location'] = u.format();