[EPS] Fix crash at app shutdown (being tried to persist clipboard image)
Summary:
Deny any capabilities when there is no QApp instance.
BUG: 397040
Test Plan:
Untested, as I do not experience the bug on my system and had no time to
invest into trying to.
Reviewers: zccrs, dfaure, pino
Reviewed By: dfaure
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D15405