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)

throw new Error("Bounding box is required.");
    }
    
    
    let bounds = Util.getAxialAlignedBoundingBox(
      group.bbox,
      currentCtx.mozCurrentTransform
    );
    
    const canvasBounds = [
      0,
      0,
      currentCtx.canvas.width,
      currentCtx.canvas.height,
    ];
    bounds = Util.intersect(bounds, canvasBounds) || [0, 0, 0, 0];
    
    
    const offsetX = Math.floor(bounds[0]);
    const offsetY = Math.floor(bounds[1]);
    let drawnWidth = Math.max(Math.ceil(bounds[2]) - offsetX, 1);
    let drawnHeight = Math.max(Math.ceil(bounds[3]) - offsetY, 1);
    let scaleX = 1,
      scaleY = 1;
    if (drawnWidth > MAX_GROUP_SIZE) {
      scaleX = drawnWidth / MAX_GROUP_SIZE;
      drawnWidth = MAX_GROUP_SIZE;
    }
    if (drawnHeight > MAX_GROUP_SIZE) {
      scaleY = drawnHeight / MAX_GROUP_SIZE;