fix: decode URI when previewing prerendered pages

[teemingc]

fixes #12865

The issue only affected the preview server as we weren't decoding the URI before checking if the prerendered file existed or not.

---

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

Edits

• Please ensure that 'Allow edits from maintainers' is checked. PRs without this option may be closed.

[changeset-bot]

🦋 Changeset detected

Latest commit: b22617e

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[teemingc]

Not sure why the lint fails on kit/src/exports/vite/public.d.ts since formatting that file doesn't change anything.

packages/kit lint: [warn] src/exports/public.d.ts
packages/kit lint: [warn] Code style issues found in the above file. Run Prettier to fix.

Will have to look at the other failing tests though.
EDIT: fixed by adding a try-catch when decoding the URI