Link to PDF file (or attach file here):
[pages4.pdf](https://github.com/mozilla/pdf.js/files/1128300/pages4.pdf)

Configuration:
- Web browser and its version: Firefox 54
- Operating system and its version: Win 10
- PDF.js version: 1.8.522
- Is an extension: no

What is the expected behavior? (add screenshot)
![chrome1-1 1](https://user-images.githubusercontent.com/146436/27918380-2f74512a-6245-11e7-8525-d0038fa6c2e8.jpg)
![chrome1-2 1](https://user-images.githubusercontent.com/146436/27918425-54f8e47e-6245-11e7-9bff-127f79ad0511.jpg)


What went wrong? (add screenshot)
![screenshot from 2017-07-06 12-10-30](https://user-images.githubusercontent.com/146436/27918442-5d57624e-6245-11e7-9436-5ba31cc8bd1a.png)
![screenshot from 2017-07-06 12-10-44](https://user-images.githubusercontent.com/146436/27918454-63b486da-6245-11e7-9eb5-c03aa5c40943.png)



const groupCtx = this.ctx;
    this.groupLevel--;
    this.ctx = this.groupStack.pop();
    composeSMask(this.ctx, this.current.activeSMask, groupCtx);
    this.ctx.restore();
    copyCtxState(groupCtx, this.ctx);
    
    
    const deltaTransform = Util.transform(
      this.current.activeSMask.startTransformInverse,
      groupCtx.mozCurrentTransform
    );
    this.ctx.transform.apply(this.ctx, deltaTransform);
  }
  save() {
    this.ctx.save();
    const old = this.current;
    this.stateStack.push(old);
    this.current = old.clone();
    this.current.resumeSMaskCtx = null;
  }
  restore() {