Fix naive iteration of service listing

[savetheclocktower]

My original stab at this in #125 wasn't paranoid enough. After all, we're reading from a random package.json file, and there's no guarantee that the format of that file will be what we expect.

In this case, the atom-ide-deno package detail page was 500ing because of this apparent nesting error in the JSON.

The fix is to do poor-man's validation of the JSON as we're consuming it, bailing if anything isn't what we expect.

Verification

https://web.pulsar-edit.dev/packages/atom-ide-deno will fail on main; http://localhost:8091/packages/atom-ide-deno will succeed when run locally on this PR branch.

[confused-Techie]

Looks good to me! Love the paranoia baked into this PR.

I'll go ahead and merge it when I've got time to push it's changes to prod, thanks for discovery and resolving the issue!