If you receive a message, a notification will appear. If you reply in
Empathy's chat window before the notification disappears, the
notification is updated with the contents of the message you *just*
sent! We should only update notifications if they're incoming.
https://bugzilla.gnome.org/show_bug.cgi?id=650219
Signed-off-by: Jonny Lamb <jonnylamb@gnome.org>