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
ctx.save();
        const pattern = current.fillColor.getPattern(ctx, this);
        patternTransform = ctx.mozCurrentTransform;
        ctx.restore();
        ctx.fillStyle = pattern;
      }
      ctx.transform.apply(ctx, current.textMatrix);
      ctx.translate(current.x, current.y + current.textRise);
      if (fontDirection > 0) {
        ctx.scale(textHScale, -1);
      } else {
        ctx.scale(textHScale, 1);
      }
      let lineWidth = current.lineWidth;
      const scale = current.textMatrixScale;
      if (scale === 0 || lineWidth === 0) {
        const fillStrokeMode =
          current.textRenderingMode & TextRenderingMode.FILL_STROKE_MASK;
        if (
          fillStrokeMode === TextRenderingMode.STROKE ||
          fillStrokeMode === TextRenderingMode.FILL_STROKE
        ) {
          this._cachedGetSinglePixelWidth = null;
          lineWidth = this.getSinglePixelWidth() * MIN_WIDTH_FACTOR;
        }
      } else {
        lineWidth /= scale;
      }
      if (fontSizeScale !== 1.0) {
        ctx.scale(fontSizeScale, fontSizeScale);