dbus: proper error handler should be given after send_negotiate_unix_fd failed

dbus: proper error handler should be given after send_negotiate_unix_fd failed

Once send_negotiate_unix_fd failed, this failure will happen, since
auth->guid_from_server has been set to some value before
send_negotiate_unix_fd. send_negotiate_unix_fd failure will lead to
this auth be handled by process_ok again, but this auth->guid_from_server
is not zero.

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>