fix small bug that occured when cmake was 'rerun'
fix small bug that occured when cmake was 'rerun'

radarsat1/siconos,fperignon/siconos,bremond/siconos,fperignon/siconos,siconos/siconos,bremond/siconos,siconos/siconos,siconos/siconos,siconos/siconos-deb,radarsat1/siconos,radarsat1/siconos,siconos/siconos-deb,fperignon/siconos,radarsat1/siconos,siconos/siconos-deb,fperignon/siconos,bremond/siconos,siconos/siconos-deb,siconos/siconos,radarsat1/siconos,fperignon/siconos,bremond/siconos,siconos/siconos-deb,bremond/siconos,siconos/siconos-deb