[effects/presentwindows] Activate even if only one window is open
requested to merge ngraham/kwin:activate-present-windows-effect-even-if-only-one-window-is-open into master
Requested by VDG, and fixes a minor usability issue with certain combinations of Task Manager options.
BUG: 428301 FIXED-IN: 5.22
cc @teams/vdg