KCrash: fix crash (ironic heh) when used in an app without QCoreApplication
Summary:
For instance in kio_help. The right fix is to create a QCoreApplication
in all kioslaves, but this commit preserves compatibility between KF 5.50
and 5.51 after KIO's commit d428fc8e6447ede81f1e1911d0b66b39265672f3
Test Plan: Starting khelpcenter, no more core files from kio_help in my cores directory.
Reviewers: heikobecker, aacid, sitter
Reviewed By: heikobecker
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D16183
(cherry picked from commit 6dbd0edec10f65ff00341ccca94a052bbd55a876)