slapos_panel: do not crash if document is not linked to a project

master/bt5/slapos_panel/SkinTemplateItem/portal_skins/slapos_panel/Base_hasSlapOSProjectUserGroup.py

@@ -9,6 +9,9 @@ elif project_relation == 'destination_project':
 else:
   raise ValueError('Unexpected project relation: %s' % project_relation)
 
+if project is None:
+  return None
+
 project_reference = project.getReference()
 
 member = portal.portal_membership.getAuthenticatedMember()