swipe-tracker: Guard all swipeable access with NULL
This avoids a
GLib-GObject-FATAL-CRITICAL: g_object_set_data: assertion 'G_IS_OBJECT (object)' failed
when the weak ref is already gone.
This avoids a
GLib-GObject-FATAL-CRITICAL: g_object_set_data: assertion 'G_IS_OBJECT (object)' failed
when the weak ref is already gone.