Adding a missing Port validation for the target URL when the user has PROXY settings enabled

Hello I found a missing port validation ***(check if options.port isNan)*** in the ***_proxyRequest*** function, I ran into this thing a few days ago while I was testing launchpad as an OpenID provider (https://login.launchpad.net/) through a proxy (http://web-proxy-pa.hpl.hp.com) you can see the example down below


Old (before fix);
```
var options = {"host":"http://web-proxy-pa.hpl.hp.com","port":8080,"headers":"Accept":"application/xrds+xml,text/html,text/plain,*/*","Host":"login.launchpad.net:NaN"},"path":"https://login.launchpad.net:NaN/"}
```
New (after fix):
```
var options = {"host":"http://web-proxy-pa.hpl.hp.com","port":8080,"headers":"Accept":"application/xrds+xml,text/html,text/plain,*/*","Host":"login.launchpad.net"},"path":"https://login.launchpad.net/"}
```