Raise exception if impossible to conver to base format (OOOd). Because convertToBaseFormat is usually called upon indexing do NOT call workflow script processFile (for OOOd  failure) because it will trigger another object indexing activity, thus creating an infinitive loop and growing ZODB.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@14470 20353a03-c40f-0410-a6d1-a30d3c3de9de