client.focus.history.get: use stacking order

This should make it faster in general, and provides a better fallback in
case nothing was found.

Ref: https://github.com/awesomeWM/awesome/pull/526

lib/awful/client.lua

@@ -181,7 +181,7 @@ end
 function client.focus.history.get(screen, idx, filter)
     -- When this counter is equal to idx, we return the client
     local counter = 0
-    local vc = client.visible(screen)
+    local vc = client.visible(screen, true)
     for k, c in ipairs(client.data.focus) do
         if c.screen == screen then
             if not filter or filter(c) then