KFileItemModel: Delay emitting currentDirectoryRemoved() signal
The KCoreDirLister object is modified before KCoreDirListerCache::deleteDir() returns because the signal currentDirectoryRemoved() is emitted. This prevents removal of the deleted lister from dirData.listersCurrentlyHolding in KCoreDirListerCache::forgetDirs() when the tab is closed, which causes the crash described in the bug. Hence, the signal currentDirectoryRemoved() is delayed to ensure this does not occur.