Fix "serve" subcommand for URL encoded static files

[wdv4758h]

There is a bug in zola serve for static files. If the filename contains something that will be changed after URL encoding (e.g. CJK), then I can't access it with the builtin dev server.

For example, if I put a file like static/測試.png in the project.
Before:

http://localhost:1111/測試.png -> 404 Not Found

After:

http://localhost:1111/測試.png -> get PNG image

Not sure if there is more concern for this PR, but this change solves my issue.

---

Sanity check:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Code changes

• Are you doing the PR on the next branch?

[Keats]

Thanks!