Set an initial id for parts without slugs.
Set an initial id for parts without slugs.

This fixes a problem when trying to edit new guides.
leftees/publisher,telekomatrix/publisher,leftees/publisher,leftees/publisher,theodi/publisher,leftees/publisher,telekomatrix/publisher,theodi/publisher,theodi/publisher,alphagov/publisher,theodi/publisher,telekomatrix/publisher,telekomatrix/publisher,alphagov/publisher,alphagov/publisher