fix(css): avoid generating empty JS files when JS files becomes empty but has CSS files imported

[sapphi-red]

Description

fixes #6913
fixes #6913 (comment)
fixes #16582

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• 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.

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[sapphi-red]

/ecosystem-ci run

[vite-ecosystem-ci]

📝 Ran ecosystem CI on d8b81b4: Open

suite	result	latest scheduled
nx	❌ failure	❌ failure
vite-plugin-react-pages	✅ success	❌ failure

✅ analogjs, astro, histoire, ladle, laravel, marko, nuxt, previewjs, qwik, rakkas, sveltekit, unocss, vike, vite-plugin-pwa, vite-plugin-react, vite-plugin-react-swc, vite-plugin-svelte, vite-plugin-vue, vite-setup-catalogue, vitepress, vitest

[bluwy]

Fix looks good to me with some questions

[susnux]

• Resolves Non deterministic build with cssCodeSplit = false and css imports #16582