BusinessTemplate: Check the existence of property before re-raise

  On the automatic upgrade some bt5 (erp5_core) can be upgraded
  before erp5_property_sheets. Since, it isnt a problem if this happens
  if no Mixin configuration is present, it is better directly check the
  existence of the property on the bt5.

  In general we expect that erp5_property_sheets is upgraded before any
  other bt5 with TypeMixin definition.

product/ERP5/Document/BusinessTemplate.py

@@ -5314,6 +5314,8 @@ Business Template is a set of definitions, such as skins, portal types and categ
         # This property may not be defined if erp5_property_sheets has not been
         # upgraded yet
       except AttributeError:
+        if getattr(self, '_portal_type_type_mixin_item', None) is not None:
+          raise
         self._portal_type_type_mixin_item = PortalTypeTypeMixinTemplateItem(())