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.pendingEOFill = false;
    this.res = null;
    this.xobjs = null;
    this.commonObjs = commonObjs;
    this.objs = objs;
    this.canvasFactory = canvasFactory;
    this.webGLContext = webGLContext;
    this.imageLayer = imageLayer;
    this.groupStack = [];
    this.processingType3 = null;
    
    
    this.baseTransform = null;
    this.baseTransformStack = [];
    this.groupLevel = 0;
    this.smaskStack = [];
    this.smaskCounter = 0;
    this.tempSMask = null;
    this.contentVisible = true;
    this.markedContentStack = [];
    this.optionalContentConfig = optionalContentConfig;
    this.cachedCanvases = new CachedCanvases(this.canvasFactory);
    if (canvasCtx) {
      
      
      addContextCurrentTransform(canvasCtx);
    }
    this._cachedGetSinglePixelWidth = null;
  }
  function putBinaryImageData(ctx, imgData, transferMaps = null) {