Fix crash if the prisma client directory exists but the prisma schema doesn't

[emmatown]

Found this when writing tests for the examples. Also made it so the checking logic does fewer file system operations.

I would write a test for this but I couldn't find a nice place for it where there are tests for generating migrations or something?

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/keystonejs/keystone-next-docs/BDTHunQDPEkHigNhZg8ww29EADQQ
✅ Preview: Failed

[Deployment for fb57a06 failed]

[changeset-bot]

🦋 Changeset detected

Latest commit: fb57a06

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@keystonejs/adapter-prisma	Patch
@keystone-next/keystone	Patch
@keystonejs/test-utils	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[timleslie]

I would write a test for this but I couldn't find a nice place for it where there are tests for generating migrations or something?

At the moment we don't have tests of the migration paths. We exercise the adapter through the API tests, but these take advantage of the prototype mode, not any of the actual migration code.

Writing tests for actual migrations is something we definitely need, but can be considered out of scope for this PR 👍

[timleslie]

👍