Steps to reproduce the problem:
1. When using the demo application - https://mozilla.github.io/pdf.js/web/viewer.html, load  the document 5311693-1.pdf

[5311693-1.pdf](https://github.com/mozilla/pdf.js/files/5137225/5311693-1.pdf)

2. go to Page 16 of the document.

3.  The strip of  EKG data  appears to have an incorrect line width   under the  Multi-color heat rate chart.

4.  When the same document is generated by pdffactory ,  the artifact are not visible.

What is the expected behavior? (add screenshot)
![expected](https://user-images.githubusercontent.com/3577617/91461157-4622cb80-e84e-11ea-8e5d-750c7b4e64ae.PNG)

What went wrong? (add screenshot)
The EKG line strip  has an incorrect thickness.  the x-transform seems to stretch the line thickness.  See the  stri in the RED rectagngle of the attached behavior versus the GREEN rectangle

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
 https://mozilla.github.io/pdf.js/web/viewer.html
y: 0,
          w: width,
          h: height,
        });
      }
      this.paintInlineImageXObjectGroup(imgData, map);
    },
    paintInlineImageXObject: function CanvasGraphics_paintInlineImageXObject(
      imgData
    ) {
      if (!this.contentVisible) {
        return;
      }
      const width = imgData.width;
      const height = imgData.height;
      const ctx = this.ctx;
      this.save();
      
      ctx.scale(1 / width, -1 / height);
      const currentTransform = ctx.mozCurrentTransformInverse;
      const a = currentTransform[0],
        b = currentTransform[1];
      let widthScale = Math.max(Math.sqrt(a * a + b * b), 1);
      const c = currentTransform[2],
        d = currentTransform[3];
      let heightScale = Math.max(Math.sqrt(c * c + d * d), 1);
      let imgToPaint, tmpCanvas, tmpCtx;
      
      if (
        (typeof HTMLElement === "function" && imgData instanceof HTMLElement) ||