Revision 862734

Backport SVN commit 862727:
Fix #167851 (Preview in columns view crashes dolphin)
Another KDirLister corner case: a dirlister holding the items,
and a second dirlister does openUrl(reload) (which triggers updateDirectory())
and the first lister immediately does openUrl() (which emits cached items).
The first lister would get no items, or after fixing this wrongly, would get them twice.