reset itempos when marking feed as read only on date sort order
reset itempos when marking feed as read only on date sort order

Do not impact people using non-date sorting in article-sort-order.
Previous behaviour might have been confusing if itempos jumped.

der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat