Disabled toggling of act. switcher immediately after it has been toggled

Summary:
There is a current issue when the user presses meta+q while the
switcher is shown. It gets hidden (the switcher lost the focus) and
shown again (because the toggle method does not know it has been hidden
a moment ago.

Reviewers: mart

Subscribers: plasma-devel

Projects: Plasma

Differential Revision: https://phabricator.kde.org/D1122