libhb: don't forget to delete chapter markers after saving them in filter_loop.

Some filters will propagate them, and since filter_loop also restores them, this can result in duplicate chapters or other related issues.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5955 b64f7644-9d1e-0410-96f1-a4d463321fa5