dvdnav: Fix use after free
dvdnav: Fix use after free

Using an unsigned value makes it impossible to detect errors, which
leads to reading from a freed buffer

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