ffmpeg: Correctly handle cookies that specify a sub-domain.

This commit fixes domain matching when the cookie specifies a sub-domain but the URL that points to the video file or playlist is pointing to the top-level domain.

A reference scenario to reproduce the original bug can be found in the ffmpeg bug tracker:
https://trac.ffmpeg.org/ticket/3336
(ticket now closed)

Built ffmpeg and tested on Windows - works as expected. Cookie header is filled properly instead of (null).

I suspect this small but subtle bug may affect playing of various sources accessible via HTTP online.