Adjust suffix in server to allow redirection when needed

[avaris]

Folders without index.html has to be redirected (/foo -> /foo/) for
directory listing to work properly. Skip '/' suffix if original path
does not have it so that base class can return a redirect.

Pull Request Checklist

Resolves: #2841

• Ensured tests pass and (if applicable) updated functional test output
• Conformed to code style guidelines by running appropriate linting tools
• Added tests for changed code
• N/A Updated documentation for changed code

[justinmayer]

Many thanks for the fix, @avaris! 🏅