Merge pull request #212 from Unity-Technologies/siyaoH/1.17/lottie

fix setstate after dispose

com.unity.uiwidgets/Runtime/widgets/LottiePainter.cs

         public override Widget build(BuildContext context) {
             if (_round != 0) {
                 WidgetsBinding.instance.addPostFrameCallback((_) => {
+                    if (!mounted) {
+                        return;
+                    }
                     setState(() => {
                         _frame += Time.deltaTime;
                         if (_frame > widget._duration) {