fix: emit vite:preloadError for chunks without deps

[sapphi-red]

Description

If the loaded chunk didn't have any deps, vite:preloadError was not emitted.

For example, the event is not emitted for https://stackblitz.com/edit/vitejs-vite-ho9n9z?file=main.js,counter.js and is emitted for https://stackblitz.com/edit/vitejs-vite-eubg1i?file=main.js,counter.js
The difference between them is that counter.js imports counter.css in the latter one.

refs #12084

/cc @danielroe

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines, especially the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Update the corresponding documentation if needed.
• Ideally, include relevant tests that fail without this PR but pass with it.

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[sapphi-red]

I think we should add a section about vite:preloadError somewhere in the docs, but I'm not sure where to put this. 🤔
The related sections to vite:preloadError are:

• https://vitejs.dev/guide/features.html#async-chunk-loading-optimization
• https://vitejs.dev/guide/build.html#chunking-strategy

[patak-dev]

I think we can add the section in the docs in another PR. Maybe another section after Chunking Strategy? (we could also think of removing the vendor plugin bits from Chunking Strategy, it may not be needed there anymore)