Fix assertion when uniniting without any notifications
Fix assertion when uniniting without any notifications

The lazy initialization from commit 3dc04fa caused a small regression: When a
process would init and uninit libnotify without ever sending a notification,
_proxy was still NULL, which caused an assertion

(process:20953): GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed

Bug-Ubuntu: https://bugs.launchpad.net/bugs/570462

GNOME/libnotify,GNOME/libnotify