Fix segfault when reading cache
Fix segfault when reading cache

When erasing elements in the vector, the iterator is reset to the
wrong element.

travisred/newsbeuter,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,x4121/newsbeuter,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,travisred/newsbeuter,newsboat/newsboat,der-lyse/newsboat,x4121/newsbeuter,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,x4121/newsbeuter,der-lyse/newsboat,travisred/newsbeuter,x4121/newsbeuter,travisred/newsbeuter