demux: adaptative: compute contentlength from byterange
demux: adaptative: compute contentlength from byterange

If byterange request is done and reply does not provide
content-length reply, read will block due to keepalive.

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc