fix: doubly encoding of URLs

[Mastercuber]

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

I'm building a blog nuxt app and using the sitemap module. While reading the sitemap, I recognized that the URLs containing umlauts like ä, ö, ü, ß and also á, à etc. are invalid. They get doubly encoded. For example: /Bücher should be encoded to /B%C3%BCcher, but now it is /B%25C3%25BCcher. The latter value is generated, when the first value (/Bücher) get URL encoded twice, so decodeURI(decodeURI('B%25C3%25BCcher')) will lead to /Bücher again.

This PR is addressing this issue, also providing a test, to show that it really only gets encoded once. For this, a little helper function was introduced (isEncoded) to check if a string is already encoded or not.

I didn't add a test showing the issue, only one for the solution..

The failing eslint checks seems unrelated to the changes..

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[harlan-zw]

Cool, great fix. Thanks!