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)
````
switch (args[0]) {
        case "RadialAxial":
          const shadingId = `shading${shadingCount++}`;
          const colorStops = args[3];
          let gradient;
          switch (args[1]) {
            case "axial":
              const point0 = args[4];
              const point1 = args[5];
              gradient = this.svgFactory.createElement("svg:linearGradient");
              gradient.setAttributeNS(null, "id", shadingId);
              gradient.setAttributeNS(null, "gradientUnits", "userSpaceOnUse");
              gradient.setAttributeNS(null, "x1", point0[0]);
              gradient.setAttributeNS(null, "y1", point0[1]);
              gradient.setAttributeNS(null, "x2", point1[0]);
              gradient.setAttributeNS(null, "y2", point1[1]);
              break;
            case "radial":
              const focalPoint = args[4];
              const circlePoint = args[5];
              const focalRadius = args[6];
              const circleRadius = args[7];
              gradient = this.svgFactory.createElement("svg:radialGradient");
              gradient.setAttributeNS(null, "id", shadingId);
              gradient.setAttributeNS(null, "gradientUnits", "userSpaceOnUse");
              gradient.setAttributeNS(null, "cx", circlePoint[0]);
              gradient.setAttributeNS(null, "cy", circlePoint[1]);