Attach (recommended) or Link to PDF file here: https://d15k2d11r6t6rl.cloudfront.net/public/users/Integrators/a0a42ab5-3cb9-4912-84b7-3c6e47330d5c/smart-pr-805/Consumentenfolder_A5_zonder_paskruizen%20_2.pdf (and the similar other files under "Informatiefolder" on https://news.pressmailings.com/hvdm/partnertoolkit)

Configuration:
- Web browser and its version: Firefox 84.0 (64 bits)
- Operating system and its version: Arch Linux
- PDF.js version: 2.7.262 (built-in) and 2.7.434 (development version at time of writing)
- Is a browser extension: no

Steps to reproduce the problem:
1. Open the linked PDF file linked above.
2. Notice that the first page is rendered completely broken. There are no warnings/errors in the console unfortunately, and it's not related to layers since the document does not contain any.

What is the expected behavior? (add screenshot)
![good](https://user-images.githubusercontent.com/1993262/103363234-e158d580-4aba-11eb-9eb7-fe0db9f0a193.png)

What went wrong? (add screenshot)
![broken](https://user-images.githubusercontent.com/1993262/103363239-e4ec5c80-4aba-11eb-9f7d-3edac62ece3c.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): -
const length = maskData.length;
  const scale = 1 / 255;
  for (let i = 3; i < length; i += 4) {
    const alpha = transferMap ? transferMap[maskData[i]] : maskData[i];
    layerData[i] = (layerData[i] * alpha * scale) | 0;
  }
}
function composeSMaskLuminosity(maskData, layerData, transferMap) {
  const length = maskData.length;
  for (let i = 3; i < length; i += 4) {
    const y =
      maskData[i - 3] * 77 + 
      maskData[i - 2] * 152 + 
      maskData[i - 1] * 28; 
    layerData[i] = transferMap
      ? (layerData[i] * transferMap[y >> 8]) >> 8
      : (layerData[i] * y) >> 16;
  }
}
function genericComposeSMask(