Revalidate index page, require instant revalidation if no shop is present during build

[janus-reith]

Signed-off-by: Janus Reith [email protected]

Resolves #697
Impact: major
Type: feature|bugfix|performance|test|style|refactor|docs|chore

Issue

The shop is not present during the default CI build and no revalidation is set for that page. the shop id stays undefined and the query for catalog items is skipped.

Solution

Set a revalidation time for that page, check if no shop is present and return fallback values that will require immedate revalidation.

Testing

1. Run the production build
2. Visit the index page, no catalog items come up

Additional context

As discussed with @willopez, we should somehow make sure that this is actually discouraged for production builds, as depoyments should not feature an initial render that is blank until the revalidated page is returned for subsequent requests.

[willopez]

LGTM