Fix NPE for checking for whether animators should play together

    /**

     * @hide

     * TODO: For animatorSet defined in XML, we can use a flag to indicate what the play order

     * if defined (i.e. sequential or together), then we can use the flag instead of calculate

     * dynamically.

     * if defined (i.e. sequential or together), then we can use the flag instead of calculating

     * dynamically. Note that when AnimatorSet is empty this method returns true.

     * @return whether all the animators in the set are supposed to play together

     */

    public boolean shouldPlayTogether() {

        updateAnimatorsDuration();

        createDependencyGraph();

        // All the child nodes are set out to play right after the delay animation

        return mRootNode.mChildNodes.size() == mNodes.size() - 1;

        return mRootNode.mChildNodes == null || mRootNode.mChildNodes.size() == mNodes.size() - 1;

    }

    @Override

    PropertyAnimator* animator = new PropertyAnimator(propertyValuesHolder,

            interpolator, startDelay, duration, repeatCount);

    mAnimators.emplace_back(animator);

    setListener(new PropertyAnimatorSetListener(this));

    // Check whether any child animator is infinite after adding it them to the set.

    if (repeatCount == -1) {

    setStartValue(0);

    mLastFraction = 0.0f;

    setInterpolator(new LinearInterpolator());

    setListener(new PropertyAnimatorSetListener(this));

}

void PropertyValuesAnimatorSet::onFinished(BaseRenderNodeAnimator* animator) {

    std::sort(mAnimators.begin(), mAnimators.end(), [](auto& a, auto&b) {

        return a->getTotalDuration() < b->getTotalDuration();

    });

    mDuration = mAnimators[mAnimators.size() - 1]->getTotalDuration();

    mDuration = mAnimators.empty() ? 0 : mAnimators[mAnimators.size() - 1]->getTotalDuration();

    mInitialized = true;

}