Fix yet another oopsle

lib.lua

@@ -186,7 +186,7 @@ end
 local function collate_stacks(s)
     local out = {}
     for _, stack in pairs(s) do
-        local i = w.get_internal_identifier(stack)
+        local i = get_internal_identifier(stack)
         if out[i] then out[i].count = out[i].count + stack.count
         else out[i] = stack end
     end