[RaphaelFakhri]

With preCompressed: true and an array root, a file that exists only in the first root without a pre-compressed variant returns 404 when the request sends Accept-Encoding.

On ENOENT, the handler moved to the next root before it tried the remaining encodings in the current root, so the encoding fallback, including the uncompressed file, ran only in the last root.

This change tries the remaining encodings and then the uncompressed file in the current root before it moves to the next root. An earlier root still wins over a later one, which matches the behavior without preCompressed. It also drops the extra identity lookup that the previous checkedEncodings.has(undefined) check caused.

Fixes #628

Checklist

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

[mcollina]

lgtm

[Tony133]

lgtm