standard_error_message: Adjust exception context for Zope 4

Since Zope 4, the `standard_error_message` is rendered in the context
of REQUEST['PUBLISHED'], which in case of publishing a skin (page
template or script) in the context of a document is is the skin itself,
but for error rendering in case of erp5_web Web Site or Web Section,
we expect standard_error_message_template to always be rendered in the
context of the document, that's why we use REQUEST.PARENTS[0] as context.

REQUEST.PUBLISHED = <PythonScript at /erp5/script used for /erp5/module/document>
REQUEST.PARENTS [<Document>, <Module>, <ERP5Site>, ...]

product/ERP5/bootstrap/erp5_xhtml_style/SkinTemplateItem/portal_skins/erp5_xhtml_style/standard_error_message.py

@@ -5,7 +5,10 @@
   root is defined then it renders the error from portal.
 """
 from zExceptions import Unauthorized
+
 try:
+  # Adjust exception context for Zope 4.
+  context = container.REQUEST.get('PARENTS', [context])[0]
   return context.standard_error_message_template(*args, **kw)
 except Unauthorized:
   pass