avoid duplication of .gz suffix

[GhostCore07]

prevents an issue where when a .gz file is requested it attempts to append an additional .gz suffix prior to checking if the file exists, i.e. the extension becomes .gz.gz

Relevant issues

Contributor checklist

• [ ] Provide tests for the changes (unless documentation-only)
• [ ] Documented any new features, CLI switches, etc. (if applicable)
  • [ ] Server --help output
  • [ ] README.md
  • [ ] doc/http-server.1 (use the same format as other entries)
• [ ] The pull request is being made against the master branch

Maintainer checklist

• [ ] Assign a version triage tag
• [ ] Approve tests if applicable

[github-actions[bot]]

This pull request has been inactive for 360 days