temporary fix to prevent failing method conversion test.

--HG--
branch : mep107

myhdl/_extractHierarchy.py

@@ -318,8 +318,9 @@ class _HierExtr(object):
                     cellvars = []
                     cellvars.extend(frame.f_code.co_cellvars)
 
-                    local_gens = []
                     #All nested functions will be in co_consts
+                    if func:
+                        local_gens = []
                         consts = func.func_code.co_consts
                         for item in _flatten(arg):
                             genfunc = _genfunc(item)