Properly log off after retrieving just refs.

NEWS

@@ -34,6 +34,9 @@
  * Don't drop first slash for SSH paths, except for those
    starting with "~". (Jelmer Vernooij, René Stern, #463)
 
+ * Properly log off after retrieving just refs.
+   (Jelmer Vernooij)
+
 0.16.3	2016-01-14
 
  TEST FIXES

dulwich/client.py

@@ -630,6 +630,7 @@ class TraditionalGitClient(GitClient):
         proto, _ = self._connect(b'upload-pack', path)
         with proto:
             refs, _ = read_pkt_refs(proto)
+            proto.write_pkt_line(None)
             return refs
 
     def archive(self, path, committish, write_data, progress=None,