fix: correctly SSR hidden="until-found"

[7nik]

Closes #16750

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[changeset-bot]

🦋 Changeset detected

Latest commit: f835a57

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

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[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16773

[Rich-Harris]

TIL!