crash fix if user not logged in

```
TypeError: Cannot read property 'uid' of undefined
    at Middleware.setupRequired (/var/www/community.nodebb.org/node_modules/nodebb-plugin-pushbullet/middleware.js:30:39)
    at Layer.handle [as handle_request] (/var/www/community.nodebb.org/node_modules/express/lib/router/layer.js:76:5)
    at next (/var/www/community.nodebb.org/node_modules/express/lib/router/route.js:100:13)
    at /var/www/community.nodebb.org/src/middleware/middleware.js:236:4
    at checkComplete (/var/www/community.nodebb.org/public/src/translator.js:142:5)
    at Object.translator.translate (/var/www/community.nodebb.org/public/src/translator.js:138:3)
    at /var/www/community.nodebb.org/src/middleware/middleware.js:234:14
    at /var/www/community.nodebb.org/node_modules/async/lib/async.js:592:17
    at done (/var/www/community.nodebb.org/node_modules/async/lib/async.js:135:19)
    at /var/www/community.nodebb.org/node_modules/async/lib/async.js:32:16
```