Fix wibox to forward shapes directly

When doing w.shape_bounding = foo on a wibox, the code would first read
shape_bounding from the underlying drawin. This would create a
(possibly) huge cairo image surface that just waits to be collected by
the garbage collector, resulting in increased memory usage.

Fix this by checking the force_forward table first. This tables contains
the names of shape properties. Thus, the evaluation of this statement
gets short-circuited and the property is on the drawin is not read.

Helps-with: https://github.com/awesomeWM/awesome/issues/1958
Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/wibox/init.lua

@@ -272,7 +272,7 @@ local function new(args)
         __newindex = function(self, k,v)
             if rawget(self, "set_"..k) then
                 self["set_"..k](self, v)
-            elseif w[k] ~= nil or force_forward[k] then
+            elseif force_forward[k] or w[k] ~= nil then
                 w[k] = v
             else
                 rawset(self, k, v)