X.L.Decoration: avoid flicker by not showing decowins without rectangles
X.L.Decoration: avoid flicker by not showing decowins without rectangles


These would be hidden by updateDecos immediately after being shown. This
caused flicker with simpleTabbed and only one window on a workspace.

ohlus/xmonad-contrib,CaptainPatate/xmonad-contrib,f1u77y/xmonad-contrib,0/xmonad-contrib,mathstuf/xmonad-contrib,0/xmonad-contrib,CaptainPatate/xmonad-contrib,ohlus/xmonad-contrib,ohlus/xmonad-contrib,0/xmonad-contrib,pjones/xmonad-test,mathstuf/xmonad-contrib,mathstuf/xmonad-contrib,CaptainPatate/xmonad-contrib,xmonad/xmonad-contrib,f1u77y/xmonad-contrib,xmonad/xmonad-contrib