BobIpTinyface returns a empty list list on failure but is tested for None

There is a mismatch between how the error case of not detecting any face is raised (empty list): https://gitlab.idiap.ch/bob/bob.ip.facedetect/-/blob/db3756548da07918e7b9b4a8c2cd3dcf7783f810/bob/ip/facedetect/tinyface.py#L228 and handled (tested for None): https://gitlab.idiap.ch/bob/bob.bio.face/-/blob/ead8c069bafb4024dc15c5df7fdc878aec8bd5f0/bob/bio/face/annotator/bobiptinyface.py#L39