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)

dimy.size,
      true
    );
    const tmpCtx = tmpCanvas.context;
    const graphics = canvasGraphicsFactory.createCanvasGraphics(tmpCtx);
    graphics.groupLevel = owner.groupLevel;
    this.setFillAndStrokeStyleToContext(graphics, paintType, color);
    let adjustedX0 = x0;
    let adjustedY0 = y0;
    let adjustedX1 = x1;
    let adjustedY1 = y1;
    
    
    
    if (x0 < 0) {
      adjustedX0 = 0;
      adjustedX1 += Math.abs(x0);
    }
    if (y0 < 0) {
      adjustedY0 = 0;
      adjustedY1 += Math.abs(y0);
    }
    tmpCtx.translate(-(dimx.scale * adjustedX0), -(dimy.scale * adjustedY0));
    graphics.transform(dimx.scale, 0, 0, dimy.scale, 0, 0);
    this.clipBbox(graphics, adjustedX0, adjustedY0, adjustedX1, adjustedY1);
    graphics.baseTransform = graphics.ctx.mozCurrentTransform.slice();
    graphics.executeOperatorList(operatorList);
    graphics.endDrawing();
    return {
      canvas: tmpCanvas.canvas,