Handle file paths as not found in delivery API by route requests

[AndyButland]

Prerequisites

• I have added steps to test this contribution in the description below

Resolves: #19051

Description

As the linked issue shows, a request to the delivery API to retrieve a content item by route will fail with a 500 rather than a 404 for a file path request. This is because there's no Umbraco context available for these requests and an exception is thrown as one is expected to exist.

In this update I've checked for a file request and where found, immediately return null and hence 404 to the caller.

Note that this doesn't happen on 15 - due to the removal of the "published snapshot" - a 404 is returned already on this version. So the fix is needed only for 15.

Testing

• Make a delivery API request to an existing route, e.g. /umbraco/delivery/api/v2/content/item/my-folder/my-page, and verify the expected 200 response is returned.
• Make a delivery API request to a non-existing route, e.g. /umbraco/delivery/api/v2/content/item/my-folder/my-missing-page, and verify the expected 404 response is returned.
• Make a delivery API request to a file, e.g. /umbraco/delivery/api/v2/content/item/my-folder/my-file.txt, and verify that now a 404 response is returned.

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[kjac]

Works like a charm. Good stuff!

I renamed "resolveable" to "resolvable" - Google says that's the correct spelling 🤷