Fix: cannot access context in onSwipe when no cards left then "dest…

…roy" the widget tree (#29)

lib/src/card_swiper.dart

@@ -248,9 +248,9 @@ class _CardSwiperState<T extends Widget> extends State<CardSwiper>
 
   @override
   void dispose() {
-    super.dispose();
     _animationController.dispose();
     widget.controller?.removeListener(_controllerListener);
+    super.dispose();
   }
 
   @override