Fix respective scripts to change to that state rather than add another low priority activity (which is likely to fail again).
When in this state (conversion_failed) user has a chance to act accordingly in some use cases (bad file upload)

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@33688 20353a03-c40f-0410-a6d1-a30d3c3de9de