git-svn: avoid crashing svnserve when creating new directories
When sorting directory names by depth (slash ("/") count) and closing the deepest directories first (as the protocol requires), we failed to put the root baton (with an empty string as its key "") after top-level directories (which did not have any slashes).
This resulted in svnserve being in a situation it couldn't handle and caused a segmentation fault on the remote server.
This bug did not affect users of DAV and filesystem repositories.
Signed-off-by: Eric Wong <email@example.com> Confirmed-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>