Add a workaround for FFmpeg's color conversion accessing past the end of the buffer
Add a workaround for FFmpeg's color conversion accessing past the end of the buffer

I delete the LIBAVFORMAT_BUILD < 5231 branch, because I couldn't even find FFmpeg with
such a small build number, let alone test with it.

opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv