Let's say, there is a file `foo/index.html` and a request for `/foo`.
The first request_path line makes it `./foo`, i.e. a local relative file path.
The second request_path line then makes it `./foo/index.html`. With the line from your question it would be `foo./index.html` which does not exist.
The current version also works with the request `/foo/` (resulting in `./foo//index.html`, which still works) and `/` (resulting in `./index.html`)