view_thread only fires the first time an email in a thread is clicked on

[ek23]

Steps to reproduce:

1. Open a thread with more than one email: view_thread will fire for the latest/bottom email in the thread
2. Click the previous email in the thread: view_thread will fire for the the selected email in the thread
3. Click back to the latest/bottom: view_thread will not fire

I believe this can be fixed with the following change. Will fork and put in a PR

[ek23]

From the documentation, it looks like I have described how view_email should work rather than view_thread. view_thread has always worked fine as a replacement for view_email until recently, but I'm not sure if this fix is appropriate for view_thread. @josteink what do you think?