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)

const transparentCanvas = this.cachedCanvases.getCanvas(
        "transparent",
        width,
        height,
        true
      );
      this.compositeCtx = this.ctx;
      this.transparentCanvas = transparentCanvas.canvas;
      this.ctx = transparentCanvas.context;
      this.ctx.save();
      
      
      this.ctx.transform.apply(this.ctx, this.compositeCtx.mozCurrentTransform);
    }
    this.ctx.save();
    resetCtxToDefault(this.ctx);
    if (transform) {
      this.ctx.transform.apply(this.ctx, transform);
    }
    this.ctx.transform.apply(this.ctx, viewport.transform);
    this.baseTransform = this.ctx.mozCurrentTransform.slice();
    this._combinedScaleFactor = Math.hypot(
      this.baseTransform[0],
      this.baseTransform[2]
    );
    if (this.imageLayer) {
      this.imageLayer.beginLayout();
    }
  }
  executeOperatorList(