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)
````
const current = this.current;
      const width = imgData.width;
      const height = imgData.height;
      const fillColor = current.fillColor;
      current.maskId = `mask${maskCount++}`;
      const mask = this.svgFactory.createElement("svg:mask");
      mask.setAttributeNS(null, "id", current.maskId);
      const rect = this.svgFactory.createElement("svg:rect");
      rect.setAttributeNS(null, "x", "0");
      rect.setAttributeNS(null, "y", "0");
      rect.setAttributeNS(null, "width", pf(width));
      rect.setAttributeNS(null, "height", pf(height));
      rect.setAttributeNS(null, "fill", fillColor);
      rect.setAttributeNS(null, "mask", `url(#${current.maskId})`);
      this.defs.appendChild(mask);
      this._ensureTransformGroup().appendChild(rect);
      this.paintInlineImageXObject(imgData, mask);
    }
    paintFormXObjectBegin(matrix, bbox) {