Fix check against clients in taglist (upstream git commit aedcd90d4da41132303636ba15170b6a43cc231f) wibox.widget.systray: Special case the empty systray (upstream git commit 3dd0c442a031f174000950981154139879933ab0) systray: Small consistency fixes (upstream git commit a250dcdbe12a3afa6ffa9fbb26f8c48c7e9cc049)