2.0.3 Single.takeUntil() crashes

[skgmn]

Single<T> main;
Flowable<T> other;

main.takeUntil(other.take(1)).subscribe(...);

This pseudo-code crashes when other emits an item. SingleTakeUntil.TakeUntilOtherSubscriber.onCompleted() is called twice and second call generate a crash. Please fix this.

[akarnokd]

Please provide the crash stacktrace.

[akarnokd]

Closing via #4962