Improvements to WebSection_viewSubjectIndexRenderer, "last_subject = subject.subject" was missing, so grouping was not done. Also use the fact that catalog ignores empty string to pass language=''

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@33186 20353a03-c40f-0410-a6d1-a30d3c3de9de