Improving the display of last updated timestamp with no comment

When there are no comments on a narrow viewport, the timestamp of an issue looked very squished:
![screen shot 2014-12-16 at 21 25 00](https://cloud.githubusercontent.com/assets/1315463/5462280/53fdbe24-856a-11e4-87f2-6d30da3eaa2e.png)

This fixes it by adding a full row if there are no comments:
![screen shot 2014-12-16 at 21 25 34](https://cloud.githubusercontent.com/assets/1315463/5462289/5f5a6d30-856a-11e4-92dc-e08881f8adbd.png)