Retain path when using fallback precompressed path

[colatkinson]

If there is no brotli-encoded asset and instead only a gzip-encoded one, the code first tries to serve the brotli-encoded form and then falls back on the gzip-encoded one. When doing so, however, it uses a path name that has been overwritten which leads to the wrong file being served.

For instance, if a request is for /dir/, then pathname will first be changed to index.html. On the retry, index.html will be used as the base pathname and thus /index.html will be served instead of /dir/index.html.

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Unsure if there's a better way to fix. However, I'm hopeful that if there's a cleaner way, the test will at least demonstrate the bug more clearly.

Checklist

• [x] run npm run test and npm run benchmark
• [x] tests and/or benchmarks are included
• [x] documentation is changed or added
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct

[gurgunday]

@colatkinson I will release a patch in a bit, this seems important

[colatkinson]

@gurgunday Awesome, thank you!