Attach (recommended) or Link to PDF file here:
[Test file.pdf](https://github.com/mozilla/pdf.js/files/4656226/Test.file.pdf)

Configuration:
- Web browser and its version: Chrome Version 81.0.4044.138 (Official Build) (64-bit)
- Operating system and its version: Windows 10
- PDF.js version: latest
- Is a browser extension: no

Steps to reproduce the problem:
1. Open [https://mozilla.github.io/pdf.js/web/viewer.html](https://mozilla.github.io/pdf.js/web/viewer.html)
2. Load the provided .pdf file

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/5569382/82438616-02c3fe80-9aa2-11ea-9003-b75ea1e7aac6.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/5569382/82438640-09527600-9aa2-11ea-810b-071da7e37896.png)


const length = bytes.length;
    for (let i = 3; i < length; i += 4) {
      const alpha = bytes[i];
      if (alpha === 0) {
        bytes[i - 3] = r0;
        bytes[i - 2] = g0;
        bytes[i - 1] = b0;
      } else if (alpha < 255) {
        const alpha_ = 255 - alpha;
        bytes[i - 3] = (bytes[i - 3] * alpha + r0 * alpha_) >> 8;
        bytes[i - 2] = (bytes[i - 2] * alpha + g0 * alpha_) >> 8;
        bytes[i - 1] = (bytes[i - 1] * alpha + b0 * alpha_) >> 8;
      }
    }
  }
  function composeSMaskAlpha(maskData, layerData, transferMap) {
    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) {