The documentation of command_close_bidi_pipe() claims that it can
be called as a method, but it does not check whether the first
argument is $self or not assuming the latter. Using _maybe_self()
fixes this.
Signed-off-by: Michal Nazarewicz <mina86@mina86.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>