Hide closed discussion threads with zero comments

The discussion block is hidden for comment threads that have zero comments and are closed to avoid the following: 

![screen shot 2014-10-09 at 17 36 20](https://cloud.githubusercontent.com/assets/2236852/4580085/6cfa3150-4fd2-11e4-911c-49afbf507035.png)



prefer `bind`-ing the callback, then no need for this `self`s