Link to PDF file (or attach file here):
https://issues.apache.org/jira/secure/attachment/12650283/000004_ShadingPatternTextPDF.pdf

Configuration:
- Web browser and its version: FF 51.0.1 32bit
- Operating system and its version: W7
- PDF.js version: latest

Steps to reproduce the problem:
display file

What is the expected behavior? (add screenshot)
![ok](https://cloud.githubusercontent.com/assets/6665575/23339534/5ff2de9c-fc25-11e6-837e-0fdaf81b4ca9.png)

What went wrong? (add screenshot)
![nok](https://cloud.githubusercontent.com/assets/6665575/23339536/63f7a37e-fc25-11e6-813c-cc218cc4def3.png)

possibly similar problem:
https://www.pdflib.com/fileadmin/pdflib/Cookbook/pdf/color_gradient.pdf (shaded text completely missing)
https://issues.apache.org/jira/secure/attachment/12630566/pslib-shading.pdf (page 4, part of text missing)
https://issues.apache.org/jira/secure/attachment/12652009/pattern-shading-2-4-idMatrix.pdf (some text missing)
https://issues.apache.org/jira/secure/attachment/12652010/pattern-shading-2-4-noMatrix.pdf (some text missing)

while (this.stateStack.length || this.current.activeSMask !== null) {
      this.restore();
    }
    this.ctx.restore();
    if (this.transparentCanvas) {
      this.ctx = this.compositeCtx;
      this.ctx.save();
      this.ctx.setTransform(1, 0, 0, 1, 0, 0); 
      this.ctx.drawImage(this.transparentCanvas, 0, 0);
      this.ctx.restore();
      this.transparentCanvas = null;
    }
    this.cachedCanvases.clear();
    this.cachedCanvasPatterns.clear();
    this.cachedPatterns.clear();
    if (this.imageLayer) {
      this.imageLayer.endLayout();
    }
  }
  _scaleImage(img, inverseTransform) {