Use the pixel aspect ratio for calculate the real aspect ratio

QtAV use width / height to calculate the video aspect ratio. This work if the pixel aspect ratio is 1:1. But i experienced issues with streams with a different pixel aspect ratio.
For example i got a video with a width / height who make a ratio of 1,25 and a pixel aspect ratio of 1,42. Multiplying them together i get 1,775 that is a 16:9 video (the correct ratio for my video).

FFMpeg expose this information in this API https://ffmpeg.org/doxygen/trunk/structAVFrame.html#a62f9c20541a83d37db7072126ff0060d

This patch will fix QtAV for support that API. In my test it seem to work correctly, but i think it need more tests.