SVGLoader: fixed multiple css classes

[vojty]

Multiple CSS classes don't work with SVGLoader.

Demo

https://codesandbox.io/s/three-js-svg-multiple-classes-wdxhd

Expected

Actual

Problem

The attributes of the first class are overridden by empty strings from the next ones

Object.assign({ fill: "red" }, { fill: '' }) // produces {fill: ''}

Clearing the attributes with empty strings should be sufficient

[yomboprime]

To my knowledge the PR is correct, though I didnt code the CSS parsing part.

[mrdoob]

Thanks!

[mrdoob]

@vojty Is it possible to implement this without creating a unused var?

[vojty]

@mrdoob ah, sure #23222