x11/plasma6-layer-shell-qt: Fix crash when right-clicking the desktop
Tested by: makc, Kenneth Raplee <kenrap@kennethraplee.com>
Pull Request: https://github.com/freebsd/freebsd-ports/pull/431
(cherry picked from commit 4b46b47d31da8d6b6d87bd27903b2d8056a53b22)