dillon1000/react

Fallback to current props if memoizedProps is null

If work has progressed on a state update that gets resumed
because of another state up, then we won't have an new
pendingProps, and we also won't have any memoizedProps because
it got aborted before completing. In that case, we can just
fallback to the current props.

I think that they can't have diverged because the only way they
diverge is if there is new props.

This lets us bail out on state only updates in more cases which
the unit tests reflect.