Fix crash in scrollToEnd

[robingullo]

Description

In rare cases where the list unmounts just after a scrollToEnd, you get an unhandled TypeError: Cannot read property 'scrollToEnd' of null coming from this line:

setTimeout(function () {
    scrollViewRef.current.scrollToEnd({ animated: animated });
}, 0);

It might be a race condition with the setTimeout.

Reviewers’ hat-rack 🎩

Replacing current!.scrollToEnd with current?.scrollToEnd has no other impact since it's a side effect.

[naqvitalha]

@robingullo Thanks for catching this! Can you sign the cla? We can then pull this in.