don't make the call to open-ils.cat if there are no real copies to delete. I'm assum...

don't make the call to open-ils.cat if there are no real copies to delete.  I'm assuming we want to be able to call this method against lineitems that might not even be associated with a purchase order, much less have copies, etc.  Need to think about that permission check at the beginning which is using purchase order -> ordering agency as a context org

From my open-ils.acq.lineitem.cancel branch

git-svn-id: svn://svn.open-ils.org/ILS/trunk@16080 dcc99617-32d9-48b4-a31d-7c20da2025e4