[lines_issue.pdf](https://github.com/mozilla/pdf.js/files/3441553/lines_issue.pdf)

Configuration:
- Chrome (latest)
- Mac Os X Mojac
- PDF.js version: latest (reproduced on pdf.js demo page)

Steps to reproduce the problem:
1. Open attached pdf in pdf.js demo viewer
2. Please note that thin line in the middle is not affected by gradient, but it should be (see screenshot below taken from Mac Os X Preview)

What is the expected behavior? (add screenshot)

![image](https://user-images.githubusercontent.com/430887/62041871-5d375a00-b205-11e9-9811-97c1643ae5b9.png)

What went wrong? (add screenshot)

![image](https://user-images.githubusercontent.com/430887/62041851-51e42e80-b205-11e9-97a3-5a1ef1b20245.png)

for (const id in this.cache) {
      const canvasEntry = this.cache[id];
      this.canvasFactory.destroy(canvasEntry);
      delete this.cache[id];
    }
  }
}
function compileType3Glyph(imgData) {
  const POINT_TO_PROCESS_LIMIT = 1000;
  const width = imgData.width,
    height = imgData.height,
    width1 = width + 1;
  let i, ii, j, j0;
  const points = new Uint8Array(width1 * (height + 1));
  
  const POINT_TYPES =
      new Uint8Array([0, 2, 4, 0, 1, 0, 5, 4, 8, 10, 0, 8, 0, 2, 1, 0]);