Simplify and max_size should be a gsfuLong or dataSize should be unsigned in gsfUnpackStream

[schwehr]

    assert(max_size > 0);
    if ((buf) && (dataSize <= (gsfuLong)max_size))
    {
        memcpy(buf, dptr, dataSize);
    }
    else if ((buf) && (dataSize > (gsfuLong)max_size))
    {
        gsfError = GSF_INSUFFICIENT_SIZE;
        return (-1);
    }

Should be something more like

    if (buf) {
      if (dataSize > max_size)  {
        gsfError = GSF_INSUFFICIENT_SIZE;
        return (-1);
      } else {
        memcpy(buf, dptr, dataSize);
      }
    }