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 (isNum(glyph)) {
        spacingLength = (spacingDir * glyph * fontSize) / 1000;
        this.ctx.translate(spacingLength, 0);
        current.x += spacingLength * textHScale;
        continue;
      }
      const spacing = (glyph.isSpace ? wordSpacing : 0) + charSpacing;
      const operatorList = font.charProcOperatorList[glyph.operatorListId];
      if (!operatorList) {
        warn(`Type3 character "${glyph.operatorListId}" is not available.`);
        continue;
      }
      if (this.contentVisible) {
        this.processingType3 = glyph;
        this.save();
        ctx.scale(fontSize, fontSize);
        ctx.transform.apply(ctx, fontMatrix);
        this.executeOperatorList(operatorList);
        this.restore();
      }
      const transformed = Util.applyTransform([glyph.width, 0], fontMatrix);
      width = transformed[0] * fontSize + spacing;
      ctx.translate(width, 0);
      current.x += width * textHScale;
    }
    ctx.restore();
    this.processingType3 = null;
  }
  
  setCharWidth(xWidth, yWidth) {