test: remoteAddress may be undefined

see nodejs/node#4198

test case:
``` javascript
var net = require('net');
var server = net.createServer(function(c) { //'connection' listener
  c.on('end', function() {
    console.log(c.remoteAddress);
    server.close();
  });
});
server.listen(8124, function() {
  var client = net.connect({port: 8124}, function(c) {
    client.end();
  });
});
```

Signed-off-by: Arthur Gautier <baloo@gandi.net>

test/test.js

@@ -26,6 +26,13 @@ describe('forwarded(req)', function () {
     })
     assert.deepEqual(forwarded(req), ['127.0.0.1', '10.0.0.1', '10.0.0.2'])
   })
+
+  it('should parse headers with disconnected client', function () {
+    var req = createReq(undefined, {
+      'x-forwarded-for': '10.0.0.2,, 10.0.0.1'
+    })
+    assert.deepEqual(forwarded(req), ['10.0.0.1', '10.0.0.2'])
+  })
 })
 
 function createReq(socketAddr, headers) {