Aspect ratio improvement

[VadymPinchuk]

@brianegan It would be cool to add one more improvement to Chewie. As we have autoinit - we can also add aspectRatio from controller value.
I see this as:

  double _calculateAspectRatio(BuildContext context) {
    final size = MediaQuery.of(context).size;
    final width = size.width;
    final height = size.height;

    return _controller.value.initialized
        ? _controller.value.aspectRatio
        : width > height ? width / height : height / width;
  }

It can simplify video displaying in proper shape.
Waiting for your feedback
Thanks in advance

[brianegan]

If this is working better for your vids, would be happy for another PR!

[VadymPinchuk]

@brianegan I have checked this and simplify calculation of aspect ratio for videos, but some of videos are sized strange. In some time will do a PR

[cbenhagen]

I added something similar in #260.