Make sure the new avatar is always saved
The KIO job needs to be run synchronously, otherwise the KCM might be
deleted before the job finished. This happens when closing the KCM
module with the Ok button, or when closing the System Settings window
and clicking Apply.
Test Plan: Change avatar from System Settings, then close System Settings and click Apply.
Reviewers: Plasma, jriddell
Differential Revision: https://phabricator.kde.org/D5779