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)

if (ctx.mozCurrentTransform) {
    return;
  }
  ctx._originalSave = ctx.save;
  ctx._originalRestore = ctx.restore;
  ctx._originalRotate = ctx.rotate;
  ctx._originalScale = ctx.scale;
  ctx._originalTranslate = ctx.translate;
  ctx._originalTransform = ctx.transform;
  ctx._originalSetTransform = ctx.setTransform;
  ctx._originalResetTransform = ctx.resetTransform;
  ctx._transformMatrix = ctx._transformMatrix || [1, 0, 0, 1, 0, 0];
  ctx._transformStack = [];
  try {
    
    
    
    const desc = Object.getOwnPropertyDescriptor(
      Object.getPrototypeOf(ctx),
      "lineWidth"
    );
    ctx._setLineWidth = desc.set;
    ctx._getLineWidth = desc.get;
    Object.defineProperty(ctx, "lineWidth", {
      set: function setLineWidth(width) {
        this._setLineWidth(width * LINEWIDTH_SCALE_FACTOR);
      },
      get: function getLineWidth() {