Don't redirect from talk list when no talks

Before I had the idea to add the `Event.talk_list_begins` property I
figured I'd redirect back to the home page when there were no accepted
talks. With the property this behavior isn't really needed. I was
reminded of it because the redirect was missing the `url_for`.
Merge pull request #49 from PyGotham/fix-talk-list-redirect

Don't redirect from talk list when no talks