fix: error pages with discarded promises fail to load

[PatrickG]

Fixes #14684

It seems like writing an empty chunk to the response stream is not allowed. No error is thrown but the for await just hangs, and so the whole request hangs.

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Latest commit: a017ed0

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[jackgdll]

Thank you @PatrickG! I can confirm that this fixes the issue

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-14722-svelte.vercel.app/

[benmccann]

@PatrickG it looks like you need to run pnpm format

[teemingc]

Thank you! Brilliant really