FileToWebPath for filenames containing "public"

When using assets-loader with a file containing the `public` string, the generated url (in non-concatenated mode) was not generated correctly. The `public` string was replaced by `assets` in the filename.

Ex: for the file `css/public.css`, the url `/assets/css/assets.css` was generated instead of `/assets/css/public.css`.

This PR fixes this issue.