[BUG] PSD Thumbnail is black

[DougRogers]

    ImageSpec config;
    config["oiio:UnassociatedAlpha"] = 1;
    bool success                     = false;
    auto inp                         = ImageInput::open(filePath.toStdWString(), &config);
    if (inp)
    {
        const ImageSpec &spec = inp->spec();

        ImageBuf thumb;

        inp->get_thumbnail(thumb, 0);
        if (thumb.initialized())
        {
            // data is all zero
      }
   ...

https://www.dropbox.com/s/g5pde4djl2nfcuk/_DSC0725.zip

[lgritz]

Fixed by #3668 (and, that solution in turn also needs a separate bug fix from #3666)