[Pager] Don't show a window list on hover if there is only one window
Summary: If there is only one visible window on the virtual desktop show the title directly instead of "1 Window" + one-entry list.
Test Plan:
Before:
After:
Reviewers: hein, broulik, ngraham
Reviewed By: hein, ngraham
Subscribers: mart, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D14026