Add directory existence check to CRIS import script

[frankhereford]

Issue

While standing up the VZ data model locally, I found that there are a heterogeneous set of CRIS extracts in the dev inbox; some have PDFs in them, some don't, it appears.

This small diff adds a check to utils.process_pdfs() to return early if there is not a directory of PDFs to process for a given zip.

Associated issues

nada

Testing

Import the CRIS extracts currently in the dev inbox.

---

Ship list

• Check migrations for any conflicts with latest migrations in master branch
• Confirm Hasura role permissions for necessary access
• Code reviewed
• Product manager approved

[frankhereford]

@johnclary already had a PR cooking with this fix and others: #1518. Thanks!