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)

ctx.scale(textHScale, -1);
    } else {
      ctx.scale(textHScale, 1);
    }
    let lineWidth = current.lineWidth;
    let resetLineWidthToOne = false;
    const scale = current.textMatrixScale;
    if (scale === 0 || lineWidth === 0) {
      const fillStrokeMode =
        current.textRenderingMode & TextRenderingMode.FILL_STROKE_MASK;
      if (
        fillStrokeMode === TextRenderingMode.STROKE ||
        fillStrokeMode === TextRenderingMode.FILL_STROKE
      ) {
        this._cachedGetSinglePixelWidth = null;
        lineWidth = this.getSinglePixelWidth();
        resetLineWidthToOne = lineWidth < 0;
      }
    } else {
      lineWidth /= scale;
    }
    if (fontSizeScale !== 1.0) {
      ctx.scale(fontSizeScale, fontSizeScale);
      lineWidth /= fontSizeScale;
    }
    ctx.lineWidth = lineWidth;
    let x = 0,
      i;
    for (i = 0; i < glyphsLength; ++i) {
      const glyph = glyphs[i];