Fix no-revalidate from server action

[LexSwed]

When action returns

  return json(data, { revalidate: [] })

Empty revalidation keys array is serialised into an empty string, so response.headers.get("X-Revalidate") === ''. This makes

https://github.com/solidjs/solid-router/blob/57847624fb673003f6f0d8261ca7352ff00e7480/src/data/action.ts#L152

to be an array of [''] (Playground), causing all cache keys to be revalidated.

This PR adds empty string check, defaulting to an empty array, as empty array seem to correctly stop revalidation from happening.

Very subtle behaviour that should be tested, but I couldn't find a setup for actions testing.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 415e027d04084e8a864499a564afe1be37dc6385

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[LexSwed]

I might have changed something else for this to start working, can't confirm on reproduction

[LexSwed]

It's actually my usage of actions with all the body being on the server, makes the response data not Response, skipping the check altogether.

https://github.com/solidjs/solid-router/blob/57847624fb673003f6f0d8261ca7352ff00e7480/src/data/action.ts#L150

This makes the situation with server/not server split quite complex to grasp. When running an action, cache that needs to be revalidated lives on the client. But if all action logic is on the server, handleResponse can't know which fields need to be invalidated.

[LexSwed]

Not fixing the issue I had, it was a different problem.