Extra request with protocol v2 and git ls-remote

A colleague (Jon Simons) today pointed out an interesting behavior of git ls-remote with protocol v2: it makes a second POST request and sends only a flush packet. This can be demonstrated with the following:

  GIT_CURL_VERBOSE=1 git -c protocol.version=2 ls-remote origin

The Content-Length header on the second request will be exactly 4 bytes.

I'm not sure exactly how to fix this by looking at remote-curl.c, but I suspect that we can avoid sending a request if all we're going to do is send a flush packet. If I were a bit more familiar with the code, I'd send a patch, but I'm not.

I just thought I'd point this out since it was surprising to me.