use tp_g_signal_connect_object to connect the "closed" signal on the notification
use tp_g_signal_connect_object to connect the "closed" signal on the notification

This fix a crash if the chat window is destroyed while the notification is
still displayed (#621789).

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