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
this.ctx.transform(a, b, c, d, e, f);
      this._cachedGetSinglePixelWidth = null;
    },
    
    constructPath: function CanvasGraphics_constructPath(ops, args) {
      const ctx = this.ctx;
      const current = this.current;
      let x = current.x,
        y = current.y;
      for (let i = 0, j = 0, ii = ops.length; i < ii; i++) {
        switch (ops[i] | 0) {
          case OPS.rectangle:
            x = args[j++];
            y = args[j++];
            let width = args[j++];
            let height = args[j++];
            if (width === 0 && ctx.lineWidth < this.getSinglePixelWidth()) {
              width = this.getSinglePixelWidth();
            }
            if (height === 0 && ctx.lineWidth < this.getSinglePixelWidth()) {
              height = this.getSinglePixelWidth();
            }
            const xw = x + width;
            const yh = y + height;
            ctx.moveTo(x, y);
            ctx.lineTo(xw, y);
            ctx.lineTo(xw, yh);
            ctx.lineTo(x, yh);
            ctx.lineTo(x, y);
            ctx.closePath();