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)
````
this.viewport = viewport;
      const svgElement = this._initialize(viewport);
      return this.loadDependencies(operatorList).then(() => {
        this.transformMatrix = IDENTITY_MATRIX;
        this.executeOpTree(this.convertOpList(operatorList));
        return svgElement;
      });
    }
    convertOpList(operatorList) {
      const operatorIdMapping = this._operatorIdMapping;
      const argsArray = operatorList.argsArray;
      const fnArray = operatorList.fnArray;
      const opList = [];
      for (let i = 0, ii = fnArray.length; i < ii; i++) {
        const fnId = fnArray[i];
        opList.push({
          fnId,
          fn: operatorIdMapping[fnId],
          args: argsArray[i],
        });
      }
      return opListToTree(opList);
    }
    executeOpTree(opTree) {