Fix OP_DELETE_ALL for search feeds
Fix OP_DELETE_ALL for search feeds

Search feeds don't have an rssurl configured so the default deletion
strategy (delete all given a url) does not work.

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