fix layout

amazing at this stage, but yet another index error
the strange (and wonderful) thing is that changing the return
of the one function just shifts the variables and everything else
stays intact. Thus are the wonders of object orientation

lib/parfait/layout.rb

@@ -62,12 +62,13 @@ module Parfait
       raise "should not rely on layout internal structure, use variable_index"
     end
 
-    # index of a variable name into the layout.
-    # layout is a list, so lowest index is 1
-    # :layout is a variable for every object, so 1 is taken for :layout
-    # still, the index is the same.
+    # index of the variable when using internal_object_get
+    # (internal_object_get is 1 based and 1 is always the layout)
     def variable_index name
-      list_index(name)
+      has = list_index(name)
+      return nil unless has
+      raise "internal error #{name}:#{has}" if has < 2
+      has - 1
     end
 
     def inspect