WeiCongcong

Remove Null check from WidgetsBinding.instance

4

`WidgetsBinding.instance` is guaranteed to be NonNull now.

Meet `Index out of range` in `copyResizeCropSquare`, when I set a non zero radius to a non square image. Usage was like `copyResizeCropSquare(img, size: size, radius: radius, antialias: true, interpolation:...

With the latest version flutter and flutter_svg, svg with a `mask` attribute could not be displayed. For example: [us_flag](https://github.com/HatScripts/circle-flags/blob/gh-pages/flags/us.svg) could not be displayed. But if the mask attribute is removed...