fix: hydration for null body http status response

[shoaibakhtar9611]

Fix for issue: 13972

Root cause:

The hydration logic in [initial_fetch](https://github.com/sveltejs/kit/blob/main/packages/kit/src/runtime/client/fetcher.js#L88C17-L88C30) constructing a Response using empty string as the response body, which is invalid for null body status codes (101, 103, 204, 205, 304) as per Fetch specs. This lead to the error:

TypeError: Failed to construct 'Response': Response with null body status cannot have body

This PR basically updates the [text()](https://github.com/sveltejs/kit/blob/main/packages/kit/src/runtime/server/page/load_data.js#L325) function:

When the response status is null body status, and the .text() result is empty string, we now:

• Skip pushing the body to fetched array
• Return undefined instead of an empty string
• Avoid capturing a body for a response that must not have one

---

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