Don't create salt file if user home directory does not exist
Reviewers: mart, fvogt
Reviewed By: mart, fvogt
Subscribers: fvogt, mgerstner, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D12909
(cherry picked from commit 06760eed821f5383d03dc83a9a077a377ba39541)