Fix crash if a component does not mixin Base

[khoerling]

• facilitate 3rd-party mixins

[mikemintz]

This seems safe to merge, but I'm curious what the scenario is in which updateComponent gets called when a component doesn't use the mixin.

[khoerling]

Good question-- it happens in util.js if QueryState is used (for subscriptions).

[mikemintz]

I mean, if a component isn't using the react-rethinkdb mixin, why would updateComponent be called?

[khoerling]

Here's the line that invokes updateComponent in this case:
https://github.com/mikemintz/react-rethinkdb/blob/master/src/QueryState.js#L107

[mikemintz]

That makes sense. But I'm also curious exactly what a React developer would have to do in order to reproduce this crash, since to me it seems like updateComponent wouldn't be called on components that don't use the mixin.