Cleanup property_sheet_generating_portal_type_set

Whatever the reason we exit this code, we are not generating this portal
type anymore. So remove it from set.

product/ERP5Type/dynamic/portal_type_class.py

@@ -204,7 +204,7 @@ def generatePortalTypeClass(site, portal_type_name):
     #     "Filling accessor holder list for portal_type " + portal_type_name)
 
     property_sheet_generating_portal_type_set.add(portal_type_name)
-
+    try:
       # Initialize ZODB Property Sheets accessor holders
       accessor_holder_list = createAllAccessorHolderList(site,
                                                          portal_type_name,
@@ -217,7 +217,7 @@ def generatePortalTypeClass(site, portal_type_name):
         attribute_dict['constraints'].extend(accessor_holder.constraints)
 
       attribute_dict['_categories'] = list(base_category_set)
-
+    finally:
       property_sheet_generating_portal_type_set.remove(portal_type_name)
 
   # LOG("ERP5Type.dynamic", INFO,