Remove early bail and 404 for empty sitemaps

[devansh016]

Removed the code block that forced a 404 response when the sitemap URL list was empty. This change allows empty sitemaps to return a valid XML structure instead of a 404 error, improving visibility for users and search engines.

This aligns with user expectations and provides clearer feedback in tools like Google Search Console.

Trac ticket: https://core.trac.wordpress.org/ticket/61293

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[github-actions]

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[github-actions]

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[sybrew]

https://core.trac.wordpress.org/ticket/61293 is a duplicate of https://core.trac.wordpress.org/ticket/51912