After the split of libdvdcss from libdvdread,
the stream callback code was moved to libdvdcss.

This went largely unnoticed because most consumers
played their DVD‌ ISO images on the systems with libdvdcss
installed.

However, I tested Kodi by playing unencrypted DVD‌ ISO
and noticed the inability to play it.

This code is inspired by stream_* functions in libdvdcss.

Signed-off-by: Vasyl Gello <vasek.gello@gmail.com>