Don't show "Topic: " in tooltips if there is none
Don't show "Topic: " in tooltips if there is none

I think I made this regress when I made Empathy understand the new
Subject interface.

https://bugzilla.gnome.org/show_bug.cgi?id=683453

GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets