Use a correct emblem icon for readonly files and folders
Test Plan: Browsed some read-only files and folders with Dolphin. No visual change with Breeze or Oxygen icons. Didn't test other themes, but according to the bug report, this should fix an issue for them.
Reviewed By: broulik
Subscribers: broulik, kde-frameworks-devel
Differential Revision: https://phabricator.kde.org/D13597