configure script not found in extracted archive

[Manu N]

Hello,
I'm currently trying to setup a Portfile for libltc
(https://github.com/x42/libltc/releases).
I have setup my local repository from which I am testing.
Here's my Portfile attempt :

# -*- coding: utf-8; tab-width: 4; indent-tabs-mode: nil;
c-basic-offset: 4 -*- vim:fenc=utf-8:et:sw=4:ts=4:sts=4
# $Id$

PortSystem          1.0
PortGroup           github 1.0

github.setup        x42 libltc 1.3.0 v

revision            0
categories          audio
platforms           darwin
license             LGPL-3
maintainers         gmail.com:audionuma openmaintainer

description         libltc provides functionality to encode and decode
LTC audio.

long_description    long desc todo

checksums           rmd160  8e82a7855a0bf0c5fa5c0328f7cec9d064fd7847 \
                     sha256
2206b9d4529a6f2c2cef82f8c8bcfecabf3394a164761c9ed7b845b1afe9a8b3

Some tests :

$ sudo port -v -t destroot libltc
--->  Fetching distfiles for libltc
--->  Verifying checksums for libltc
--->  Checksumming libltc-1.3.0.tar.gz
--->  Extracting libltc
--->  Extracting libltc-1.3.0.tar.gz
Executing:  cd "/opt/local/var/macports/build/_Users_manuelnaudin_ports_audio_libltc/libltc/work"
&& /usr/bin/gzip -dc
'/opt/local/var/macports/distfiles/libltc/libltc-1.3.0.tar.gz' |
/usr/bin/tar -xf -
--->  Configuring libltc
Executing:  cd "/opt/local/var/macports/build/_Users_manuelnaudin_ports_audio_libltc/libltc/work/libltc-1.3.0"
&& ./configure --prefix=/opt/local
sh: ./configure: No such file or directory
Command failed:  cd
"/opt/local/var/macports/build/_Users_manuelnaudin_ports_audio_libltc/libltc/work/libltc-1.3.0"
&& ./configure --prefix=/opt/local
Exit code: 127
Error: Failed to configure libltc: configure failure: command execution failed
Error: See /opt/local/var/macports/logs/_Users_manuelnaudin_ports_audio_libltc/libltc/main.log
for details.
Error: Follow https://guide.macports.org/#project.tickets to report a bug.
Error: Processing of port libltc failed

Indeed, the `configure` script is not present in the
`/opt/local/var/macports/build/_Users_manuelnaudin_ports_audio_libltc/libltc/work/libltc-1.3.0`
directory.
If I automagically extract the archive with a double click in the
finder, the content of the archive is different of the content of the
macports extracted archive. And the `configure` script is here.
 Am I missing some option in the Portfile ?
(Unfortunately, there's no `/opt/local/var/macports/` dir in my
installation to check logs).

Thanks.
Manuel