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)

++count;
  }
  for (j = 1; j < width; j++) {
    if (data[pos] !== data[pos + 1]) {
      points[j0 + j] = data[pos] ? 4 : 8;
      ++count;
    }
    pos++;
  }
  if (data[pos] !== 0) {
    points[j0 + j] = 4;
    ++count;
  }
  if (count > POINT_TO_PROCESS_LIMIT) {
    return null;
  }
  
  const steps = new Int32Array([0, width1, -1, 0, -width1, 0, 0, 0, 1]);
  const outlines = [];
  for (i = 0; count && i <= height; i++) {
    let p = i * width1;
    const end = p + width;
    while (p < end && !points[p]) {
      p++;
    }
    if (p === end) {
      continue;
    }
    const coords = [p % width1, i];
    const p0 = p;