Attach (recommended) or Link to PDF file here: https://www.recom-power.com/pdf/Powerline-AC-DC/RAC05-K.pdf

Configuration:
- Web browser and its version: Firefox 56.0 (64-bit)
- Operating system and its version: Windows 10 with OS Build 15063.632
- PDF.js version: ?
- Is an extension: Built-in

Steps to reproduce the problem:
1. Open Page

What is the expected behavior? To properly render the first page. 
![image](https://user-images.githubusercontent.com/1151969/31415345-b1504022-add7-11e7-855b-8030a308f7a2.png)

What went wrong? Renders poorly.
![image](https://user-images.githubusercontent.com/1151969/31415363-d8842096-add7-11e7-818d-728c1102891b.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): ?

offsetY,
        scaleX,
        scaleY,
        subtype: group.smask.subtype,
        backdrop: group.smask.backdrop,
        transferMap: group.smask.transferMap || null,
        startTransformInverse: null, 
      });
    } else {
      
      
      currentCtx.setTransform(1, 0, 0, 1, 0, 0);
      currentCtx.translate(offsetX, offsetY);
      currentCtx.scale(scaleX, scaleY);
    }
    
    
    copyCtxState(currentCtx, groupCtx);
    this.ctx = groupCtx;
    this.setGState([
      ["BM", "source-over"],
      ["ca", 1],
      ["CA", 1],
    ]);
    this.groupStack.push(currentCtx);
    this.groupLevel++;
    
    this.current.activeSMask = null;
  }
  endGroup(group) {