Make use of tp_strdiff() to be NULL-safe. Fixes bug #509656.
Make use of tp_strdiff() to be NULL-safe. Fixes bug #509656.

svn path=/trunk/; revision=558

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