Allow PROPFIND request with empty request body

[greensea]

A request body is not mandatory in PROPFIND request according to https://www.rfc-editor.org/rfc/rfc4918#section-9.1
If the client does not send a request body, the request should be treated as an AllProp request.

[emersion]

The server is not guaranteed to return a ContentLength header field though. It would be better to check for the io.EOF error instead.

[greensea]

I am confused. The ContentLength is a request attribute, not a response header.

A client may send a request with an empty body, and the http.Request.ContentLength is 0. The patched code check this ContentLength property and make the request treated as an AllProp request.

[emersion]

Sorry, I got things mixed up: the client can omit the Content-Length header, but still provide a non-empty request body.

[emersion]

Superseded by b043bbd