fix activity runner
Summary:
Activity runner is now useless:
m_activities is always nullptr in ActivityRunner::run because ActivityRunner::down is called after ActivityRunner::match which makes activity changing impossible
Reviewers: broulik, ngraham, davidedmundson
Reviewed By: ngraham, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D27367