systemtray: Don't propagate unhandled wheel events

Authored by drosca on Dec 2 2016, 7:47 PM.

Description

systemtray: Don't propagate unhandled wheel events

Scrolling over empty space or applet that doesn't handle
wheel events no longer activates desktop containment actions.

Differential Revision: https://phabricator.kde.org/D3572

Details