Move model.req statement inside of if block

The [last commit](https://github.com/codeparty/racer/commit/c4bd5fb44d97c4497f2a6c1a569526a0c8aa3a5f) breaks Racer with the following error.

```
(master)PhishVids-public dsaewitz$ node phishvids.js 
   info  - socket.io started
Starting cluster with 1 workers in development mode
`kill -s SIGUSR2 53795` to force cluster reload
Go to: http://localhost:3000/
   info  - socket.io started
TypeError: Cannot set property 'req' of undefined
    at IncomingMessage.getModel (/Users/dsaewitz/y/PhishVids-public/node_modules/racer/lib/session/session.Store.js:94:15)
    at createPage (/Users/dsaewitz/y/PhishVids-public/node_modules/derby/lib/derby.server.js:93:21)
    at Object.middleware [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/derby/node_modules/tracks/lib/index.js:55:18)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at Object.modelMiddleware [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/racer/lib/session/session.Store.js:104:5)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at Object.session [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/connect/lib/middleware/session.js:298:7)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at Object.cookieParser [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/cookieParser.js:60:5)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at Object.methodOverride [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/methodOverride.js:37:5)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at multipart (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/multipart.js:64:37)
    at module.exports (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/bodyParser.js:57:9)
    at urlencoded (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/urlencoded.js:51:37)
    at module.exports (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/bodyParser.js:55:7)
    at json (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/json.js:53:37)
    at Object.bodyParser [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/bodyParser.js:53:5)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at Object.module.exports [as handle] (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/compress.js:145:5)
    at next (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/proto.js:190:15)
    at resume (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/static.js:60:7)
    at SendStream.error (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/connect/lib/middleware/static.js:73:37)
    at SendStream.EventEmitter.emit (events.js:126:20)
    at SendStream.error (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/send/lib/send.js:147:51)
    at SendStream.onStatError (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/send/lib/send.js:248:48)
    at SendStream.pipe (/Users/dsaewitz/y/PhishVids-public/node_modules/express/node_modules/send/lib/send.js:320:26)
    at Object.oncomplete (fs.js:297:15)
```

This merely moves that code block into the if statement below to ensure that `model` exists.