[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)

this.setLeading(-y);
      this.moveText(x, y);
    }
    setTextMatrix(a, b, c, d, e, f) {
      this.current.textMatrix = [a, b, c, d, e, f];
      this.current.textMatrixScale = Math.hypot(a, b);
      this.current.x = this.current.lineX = 0;
      this.current.y = this.current.lineY = 0;
    }
    nextLine() {
      this.moveText(0, this.current.leading);
    }
    paintChar(character, x, y, patternTransform, resetLineWidthToOne) {
      const ctx = this.ctx;
      const current = this.current;
      const font = current.font;
      const textRenderingMode = current.textRenderingMode;
      const fontSize = current.fontSize / current.fontSizeScale;
      const fillStrokeMode =
        textRenderingMode & TextRenderingMode.FILL_STROKE_MASK;
      const isAddToPathSet = !!(
        textRenderingMode & TextRenderingMode.ADD_TO_PATH_FLAG
      );
      const patternFill = current.patternFill && !font.missingFile;
      let addToPath;
      if (font.disableFontFace || isAddToPathSet || patternFill) {
        addToPath = font.getPathGenerator(this.commonObjs, character);
      }