Fix race condition when window is closed with active notifications

A ToxWindow's notifications need to be halted before the window is freed

src/chat.c

@@ -152,6 +152,7 @@ void kill_chat_window(ToxWindow *self, Tox *m)
     free(statusbar);
 
     disable_chatwin(self->num);
+    kill_notifs(self->active_box);
     del_window(self);
 }