Attach (recommended) or Link to PDF file here:
[shading_pattern.pdf](https://github.com/mozilla/pdf.js/files/1532598/shading_pattern.pdf)

Configuration:
- Web browser and its version: Firefox 57.0
- Operating system and its version: Debian GNU/Linux 9 64-bit
- PDF.js version: tried with Firefox's 1.9.583 and with online viewer 2.0.185
- Is a browser extension: no

Steps to reproduce the problem:
1. Open the attached file with the online viewer https://mozilla.github.io/pdf.js/web/viewer.html

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/11061462/33626267-d9a57dee-d9d8-11e7-8712-cfa17c038259.png)
(Image captured from Adobe Reader CS.) The shading needs to be inside the letters.

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/11061462/33626285-eaabd462-d9d8-11e7-94e2-96480b57750d.png)
The shading seems to be displaced and upside-down, for it does not cover all the characters of the word.

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

this.lineX = 0;
    this.lineY = 0;
    
    this.charSpacing = 0;
    this.wordSpacing = 0;
    this.textHScale = 1;
    this.textRenderingMode = TextRenderingMode.FILL;
    this.textRise = 0;
    
    this.fillColor = "#000000";
    this.strokeColor = "#000000";
    this.patternFill = false;
    
    this.fillAlpha = 1;
    this.strokeAlpha = 1;
    this.lineWidth = 1;
    this.activeSMask = null;
    this.transferMaps = null;
    this.startNewPathAndClipBox([0, 0, width, height]);
  }
  clone() {
    const clone = Object.create(this);
    clone.clipBox = this.clipBox.slice();
    return clone;
  }
  setCurrentPoint(x, y) {
    this.x = x;
    this.y = y;
  }
  updatePathMinMax(transform, x, y) {