Steps to reproduce (this PDF):
[page4.pdf](https://github.com/mozilla/pdf.js/files/5990272/page4.pdf)

````
npm install
node_modules/.bin/gulp dist-install
node examples/node/pdf2svg.js /tmp/page4.pdf
````

Error:
````
Error: Invalid SVG dimensions
    at unreachable (/tmp/pdf.js/build/dist/legacy/build/pdf.js:2086:9)
    at assert (/tmp/pdf.js/build/dist/legacy/build/pdf.js:2091:5)
    at DOMSVGFactory.create (/tmp/pdf.js/build/dist/legacy/build/pdf.js:640:24)
    at SVGGraphics._makeTilingPattern (/tmp/pdf.js/build/dist/legacy/build/pdf.js:24178:36)
    at SVGGraphics._makeColorN_Pattern (/tmp/pdf.js/build/dist/legacy/build/pdf.js:24127:23)
    at SVGGraphics.setFillColorN (/tmp/pdf.js/build/dist/legacy/build/pdf.js:24088:39)
    at SVGGraphics.executeOpTree (/tmp/pdf.js/build/dist/legacy/build/pdf.js:23634:22)
    at /tmp/pdf.js/build/dist/legacy/build/pdf.js:23508:18
    at process._tickCallback (internal/process/next_tick.js:68:7)
    at Function.Module.runMain (internal/modules/cjs/loader.js:834:11)
````
tiling.setAttributeNS(null, "height", tystep);
      tiling.setAttributeNS(null, "x", `${tx0}`);
      tiling.setAttributeNS(null, "y", `${ty0}`);
      
      const svg = this.svg;
      const transformMatrix = this.transformMatrix;
      const fillColor = this.current.fillColor;
      const strokeColor = this.current.strokeColor;
      const bbox = this.svgFactory.create(tx1 - tx0, ty1 - ty0);
      this.svg = bbox;
      this.transformMatrix = matrix;
      if (paintType === 2) {
        const cssColor = Util.makeHexColor(...color);
        this.current.fillColor = cssColor;
        this.current.strokeColor = cssColor;
      }
      this.executeOpTree(this.convertOpList(operatorList));
      
      this.svg = svg;
      this.transformMatrix = transformMatrix;
      this.current.fillColor = fillColor;
      this.current.strokeColor = strokeColor;
      tiling.appendChild(bbox.childNodes[0]);
      this.defs.appendChild(tiling);
      return `url(#${tilingId})`;
    }
    /**
     * @private
     */
    _makeShadingPattern(args) {