System settings: make date/time format preview consistent
Summary: BUG: 398493
Reviewers: hein, VDG, davidedmundson
Reviewed By: VDG, davidedmundson
Subscribers: GB_2, davidedmundson, abetts, ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D15423