hls: Fixing backward seek
hls: Fixing backward seek

Fixes #6261
Signed-off-by: Hugo Beauzée-Luyssen <aafaa30316387d0d59e778c546eef5bcc5f6925a@gmail.com>

shyamalschandra/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc,xkfz007/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,shyamalschandra/vlc,jomanmuk/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,xkfz007/vlc,xkfz007/vlc