Avoid empty zip on csv export, refs #10907
Avoid empty zip on csv export, refs #10907

Previously, if you went to export a csv of archival descriptions but no
descriptions matched the criteria (e.g. exporting with 'export drafts'
unchecked but only draft records are in the clipboard), AtoM would create a
blank .zip file instead of indicating to the user that no matching records
were found to be exported.

This fix rectifies that situation.

artefactual/atom,artefactual/atom,artefactual/atom