Error handling: Out of bounds post ID leads to undefined exception

[frolino]

How to replicate:

1. Click on "Posts" while in the main page.
2. Click on one of the posts. This will cause the post to show up on the right side.
3. In the address bar, change the post ID in the URL to an out-of-bounds post ID (i.e., the URL is of the form index.html#/posts/{id}, so change {id} to a post ID that doesn't correspond to any of the posts). Click enter.
4. Refresh the page. This will case a blank page to appear, and the exception "a is undefined" is thrown by JavaScript.