SVGLoader: fix round rects when only rx or ry is specified

[nkrkv]

The current implementation handles rect rounded corners incorrectly when either rx or ry attr is omitted.

Here’s a SVG made in Inkscape where only rx is specified:

round-rect.svg.zip

    <rect
       style="fill:none;stroke:#000000;stroke-width:1;stroke-linecap:square;stroke-linejoin:round"
       id="rect846"
       width="161.13248"
       height="78.283867"
       x="20.170506"
       y="27.046577"
       rx="10" />

Here’s how a browser renders it:

Here’s how THREE.js loads it without the fix:

And here’s how THREE.js loads it with the fix:

---

Indeed, the standard says:

When the computed value of ‘rx’ is auto, the used radius is equal to the absolute length used for ry, creating a circular arc.

The same applies to ry

[mrdoob]

Thanks!