Don't take ownership of KDirLister in KDirModelWhen 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.
When KDirModel is destroyed, it also deleted the dirlister, but KCoreDirListerCache didn't knew anythUsing about this deletionQPointer, and when it consulted it can detect when dirlistersCurrentlyHolding in slotRedirection resulted always in a crashr 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 ]]