Handle folder names containing spaces correctly in the Folders Panel

The problem was that KFileItemModel::setExpanded() used KUrl::url()
to determine the names of the subfolders. This method encodes special
characters, such that comparing the folder names with the unencoded URLs
stored in the model fails.
Using KUrl::path(), which does not encode special characters, fixes the
problem.

CCBUG: 291781
FIXED-IN: 4.8.1
(cherry picked from commit 80d9bfec)