Lack of transparency in some game images

[timkurvers]

Some game images exhibit a black background and lack transparency:

This could be a bug/issue in our usage of libblp from BLPConverter.

Alternatively it could be an issue with how Spelunker converts a single mipmap to a transparent PNG:

BLP.from(req.resource.data, (blp) => {
  const mipmap = blp.largest;

  const png = new PNG({ width: mipmap.width, height: mipmap.height });
  png.data = mipmap.rgba;

  res.type('image/png');
  png.pack().pipe(res);
});