hlsdemux: Fix for URLs that contain a '/' in the query parameter

hlsdemux: Fix for URLs that contain a '/' in the query parameter

If the URL for the master manifest files contains a '/' character
in the query parameter (for example
http://example.net/1054559_h264_1500k.mp4/master.m3u8?acl=/*1054559_h264_1500k.mp4),
hlsdemux is incorrectly converting the relative URLs of the media
playlists in to absolute URLs. It is incorrectly using the last '/' it
finds in the URL. According to RFC3986 the '/' character is allowed in
the query part of the URL.

https://bugzilla.gnome.org/show_bug.cgi?id=725137