catch undefined for leftArgs[0] and rightArgs[0]

[karlhaas]

Fix for #115

[alancutter]

Thanks for writing up this fix for us!
Before we can accept your submission we require you sign the Contributor License Agreement. Sorry for the hassle.

I think it might be better to change

web-animations-js/src/matrix-decomposition.js

Line 124 in 5f3d17f

return false;

to return null instead for consistency with itself.
It should also be relatively simple to add a test for this bug as well in https://github.com/web-animations/web-animations-js/blob/5f3d17fbb60dd82a3775f0c7fd7667f787096deb/test/js/transform-handler.js by giving it something like matrix(0, 0, 0, 0, 0, 0) as one of the keyframe inputs.

[karlhaas]

It says "It looks like you've already signed this CLA". I'm not really familiar with the source and just fixed the problem I found by debugging the source (it would have been easier if there would have been a non minified version of the bundle ;) )
Maybe someone who knows the code base better should provide further improvements.

[alancutter]

Maybe someone who knows the code base better should provide further improvements.

Landed a fix in #121, thanks again for doing the initial investigation!