[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)

return undefined;
      }
      const ctx = this.ctx;
      const fontSizeScale = current.fontSizeScale;
      const charSpacing = current.charSpacing;
      const wordSpacing = current.wordSpacing;
      const fontDirection = current.fontDirection;
      const textHScale = current.textHScale * fontDirection;
      const glyphsLength = glyphs.length;
      const vertical = font.vertical;
      const spacingDir = vertical ? 1 : -1;
      const defaultVMetrics = font.defaultVMetrics;
      const widthAdvanceScale = fontSize * current.fontMatrix[0];
      const simpleFillText =
        current.textRenderingMode === TextRenderingMode.FILL &&
        !font.disableFontFace &&
        !current.patternFill;
      ctx.save();
      let patternTransform;
      if (current.patternFill) {
        
        
        ctx.save();
        const pattern = current.fillColor.getPattern(ctx, this);
        patternTransform = ctx.mozCurrentTransform;
        ctx.restore();
        ctx.fillStyle = pattern;
      }
      ctx.transform.apply(ctx, current.textMatrix);
      ctx.translate(current.x, current.y + current.textRise);