I attempted to make sure I receive email for all messages and ran into a
crash. In detectors/nosyreaction.py I added my email to the nosymessage
call. When nobody is subscribed to the issue (unassigned, nobody nosy)
roundup crashes when you do this. The fix is simple and a patch is attached.

The current code crashes because smtp_send is called with an empty list
(sendto) which throws an exception when smtplib.sendmail is called
eventually. The patch just prevents smtp_send from being called if
sendto is empty.