Polyfill wrongly throws if one argument is a function

[webbedspace]

Theres nothing in the spec that says that functions can't be passed to Object.assign as either source or target (the abstract operation ToObject leaves functions unmodified), but this polyfill throws for either case. :(

It also wrongly throws if passed primitives, when in fact it should call Object() on them and use that result in their place.

[ljharb]

Hmm, that's a good point. Fixing now, thanks!