When KDirModel is destroyed, it also deletes the dirlister, but KCoreDirListerCache didn't knew anything about this deletion, and when it consulted listersCurrentlyHolding in slotRedirection resulted always in a crash.
Using QPointer, it can detect when dirlister has been deleted and remove it from the list.
As a side effect, it also fixes the crash I got in [[ https://phabricator.kde.org/D10989 | D10989 ]]