PR review companion to not run if nothing was uploaded in the PR text

[peterbe]

PR review companion will crash if there was no upload in the "PR test"

E.g. https://github.com/mdn/content/runs/2255769916?check_suite_focus=true

[peterbe]

Here's the "PR test" that started it https://github.com/mdn/content/runs/2255762883?check_suite_focus=true
As you can see it never ran the "Build changed content" step.

[peterbe]

Wow! It's still not supported. At least according to actions/runner#662
But there appears to be some OKish hacks.

[peterbe]

Hmm. So it's possible to "control the error" a bit. I

if (matchArtifacts.length === 0) {
  <<throw or exit non-zero so it bails>>
}

but what's the point?
If there's no way to exit the entire workflow, what's the point of messing around with things like:

      - name: Unzip what was downloaded
+       if: steps.download.conclusion == 'success'

They're not being run anyway if you have an error in the first step.

I think it's quite OK what happened in https://github.com/mdn/content/actions/runs/712480017
It failed on the first step so it didn't run any of the other steps.
It's a bit unfortunate that the redness of the error makes you think something went horribly wrong and needs attention.

For that, I'm going to just re-arrange and rewrite the error because Unhandled error: TypeError: Cannot read property 'id' of undefined looks like it's unintended and not in control.