The locked overlay should be added also for directories, as there is no
distinct "unreadable directory" icon.
No overlay icon for "gzip files with .gz file ending", there is a
mimetype icon for gzip files.

Backport of 877fdcd9fcbdf8267ce509d8918e5cb5a1a455aa from kio

CCBUG: 339193
REVIEW: 120606