publish() should not create a new SLUG if the supplementaries.zip is added afterwards

[dicook]

If a paper is publish()d when the Suppl: lines is non-existent, the pdf will be created, and no supplementaries.zip.

If this is a mistake, that there really should be supplementary material, so the Suppl: is then populated and the publish() is re-run, a new Slug is generated, a new folder is created on rjournal.github.io and a separate entry gets added to _config.yml

What should happen is the old Slug is used, the yaml only has the supplementary materials line updated, and the supplementaries.zip file is added to existing rjournal.github.io folder.