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)
````
x += fontDirection * wordSpacing;
          continue;
        } else if (isNum(glyph)) {
          x += (spacingDir * glyph * fontSize) / 1000;
          continue;
        }
        const spacing = (glyph.isSpace ? wordSpacing : 0) + charSpacing;
        const character = glyph.fontChar;
        let scaledX, scaledY;
        let width = glyph.width;
        if (vertical) {
          let vx;
          const vmetric = glyph.vmetric || defaultVMetrics;
          vx = glyph.vmetric ? vmetric[1] : width * 0.5;
          vx = -vx * widthAdvanceScale;
          const vy = vmetric[2] * widthAdvanceScale;
          width = vmetric ? -vmetric[0] : width;
          scaledX = vx / fontSizeScale;
          scaledY = (x + vy) / fontSizeScale;
        } else {
          scaledX = x / fontSizeScale;
          scaledY = 0;
        }
        if (glyph.isInFont || font.missingFile) {
          current.xcoords.push(current.x + scaledX);
          if (vertical) {
            current.ycoords.push(-current.y + scaledY);
          }
          current.tspan.textContent += character;