Fix selection of last unread article
Fix selection of last unread article

Issue #904 : when there is only one unread article left and it's not in
the current folder selection, the 'next unread' command did not work.

josh64x2/vienna-rss,barijaona/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,Eitot/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,Eitot/vienna-rss,ViennaRSS/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss,lapcat/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,lapcat/vienna-rss,barijaona/vienna-rss,lapcat/vienna-rss,josh64x2/vienna-rss,josh64x2/vienna-rss,lapcat/vienna-rss,ViennaRSS/vienna-rss,Eitot/vienna-rss,Eitot/vienna-rss