dvdreadsrc: correctly set next cell when seeking to sector
dvdreadsrc: correctly set next cell when seeking to sector

fluendo/gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer-sdk__gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer-sdk__gst-plugins-ugly,fluendo/gst-plugins-ugly,fluendo/gst-plugins-ugly,freedesktop-unofficial-mirror/gstreamer-sdk__gst-plugins-ugly