CreateDefaultSubobject with SubClassOf

this works, I hate it, but it works, needed an error message and forced return in PostInitializeComponents() to prevent a crash.

used FindComponentByClass<T>() where it has the cast built in.

void AMyActor::PostInitializeComponents()
{
    Super::PostInitializeComponents();
    if( ActorComp == nullptr )
    {
        if( !(ActorComp = FindComponentByClass<UMyActorComp>()) )
        {
			UE_LOG(LogTemp, Error, TEXT("ActorComp unassigned for blueprint of %s"), *GetName());
			return;
        }
    }
}