dvdreadsrc: correctly determine last chapter's duration
dvdreadsrc: correctly determine last chapter's duration

This (mostly) reverts 683f5eeae7b830e4e4b790f3817ff6b8ce517b1c.
It worked just fine before ...

knuesel/gst-plugins-ugly,knuesel/gst-plugins-ugly,knuesel/gst-plugins-ugly