xrootd/xrdproto/dirlist: add temporary hack for empty directories
xrootd/xrdproto/dirlist: add temporary hack for empty directories

This CL adds a temporary hack for issueing kXR_dirlist requests against
empty directories.
According to the specs, an empty directory should just return the 8-byte
triplet {streamid, 0, 0}.
But when called with kXR_dstat, we don't see this.

Updates xrootd/xrootd#739.

go-hep/hep,go-hep/hep