Merge pull request #2952 from erik-f/master

wibox.container.margin: Allow nonnegative dimensions

lib/wibox/container/margin.lua

@@ -48,7 +48,7 @@ function margin:layout(_, width, height)
         local resulting_width = width - x - w
         local resulting_height = height - y - h
 
-        if resulting_width > 0 and resulting_height > 0 then
+        if resulting_width >= 0 and resulting_height >= 0 then
             return { base.place_widget_at(self._private.widget, x, y, resulting_width, resulting_height) }
         end
     end