Rescue CombinePDF::ParsingError on 8879 signature pages

[jenny-heath]

Link to pivotal/JIRA issue

What was done?

Investigation summary: I think the reason we get this error is that sometimes Hub users upload wonky PDFs as unsigned 8879 document types and our code that signs this document barfs and results in the client seeing an error page. I recreated this by finding the clients who got this error (for once the Sentry page had an ID of a record) and trying to sign one of their unsigned 8879 documents locally.

In order to avoid showing the error page I've done a very minimal fix to catch the error where we catch other errors (e.g. when the client has already signed). This isn't necessarily that helpful to the client but at least the banner says to contact support. There could be a more robust solution in future but we already have a feature that asks the Hub user to confirm that what they're uploading is an unsigned 8879 PDF, and this has only happened to 5 people.

How to test?

I added one test per signing service—basically copies of the existing tests around catching errors.

Acceptance testing proposal:

• To see existing behavior on demo: as a hub user upload a malformed PDF as an unsigned 8879 and log in as the client to sign it. See that you get an error page. To get a malformed PDF, try this one from one of the clients who got this error.
• To see the new behavior on the heroku app: do the same thing. Maybe also try uploading a legit unsigned 8879 and see that signing it still works.

Screenshots (for visual change)

before (obviously this looks different on non-dev environments):

after (the second banner):

[github-actions]

Heroku app: https://gyr-review-app-4521-1fe422b86a10.herokuapp.com/
View logs: heroku logs --app gyr-review-app-4521 (optionally add --tail)

[rickreyhsig]

This seems to be aligned with the resolution discussed in boazsegev/combine_pdf#28.

[tofarr]

I added my review to this and merged since Jenny is on leave