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)

constructor(maxSize = 0) {
    this._cache = new Map();
    this._maxSize = maxSize;
  }
  has(key) {
    return this._cache.has(key);
  }
  get(key) {
    if (this._cache.has(key)) {
      
      const value = this._cache.get(key);
      this._cache.delete(key);
      this._cache.set(key, value);
    }
    return this._cache.get(key);
  }
  set(key, value) {
    if (this._maxSize <= 0) {
      return;
    }
    if (this._cache.size + 1 > this._maxSize) {
      
      this._cache.delete(this._cache.keys().next().value);
    }
    this._cache.set(key, value);
  }
  clear() {