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 ctx = this.ctx;
    const current = this.current;
    const font = current.font;
    const fontSize = current.fontSize;
    const fontDirection = current.fontDirection;
    const spacingDir = font.vertical ? 1 : -1;
    const charSpacing = current.charSpacing;
    const wordSpacing = current.wordSpacing;
    const textHScale = current.textHScale * fontDirection;
    const fontMatrix = current.fontMatrix || FONT_IDENTITY_MATRIX;
    const glyphsLength = glyphs.length;
    const isTextInvisible =
      current.textRenderingMode === TextRenderingMode.INVISIBLE;
    let i, glyph, width, spacingLength;
    if (isTextInvisible || fontSize === 0) {
      return;
    }
    this._cachedGetSinglePixelWidth = null;
    ctx.save();
    ctx.transform.apply(ctx, current.textMatrix);
    ctx.translate(current.x, current.y);
    ctx.scale(textHScale, fontDirection);
    for (i = 0; i < glyphsLength; ++i) {
      glyph = glyphs[i];