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):

return this._getLineWidth();
      },
    });
  } catch (_) {}
  Object.defineProperty(ctx, "mozCurrentTransform", {
    get: function getCurrentTransform() {
      return this._transformMatrix;
    },
  });
  Object.defineProperty(ctx, "mozCurrentTransformInverse", {
    get: function getCurrentTransformInverse() {
      
      
      
      const [a, b, c, d, e, f] = this._transformMatrix;
      const ad_bc = a * d - b * c;
      const bc_ad = b * c - a * d;
      return [
        d / ad_bc,
        b / bc_ad,
        c / bc_ad,
        a / ad_bc,
        (d * e - c * f) / bc_ad,
        (b * e - a * f) / ad_bc,
      ];
    },
  });
  ctx.save = function ctxSave() {
    const old = this._transformMatrix;
    this._transformStack.push(old);