Fixed cleanup of nested flatMaps

@pchiusano We have discovered this issue in cleantup. Can you take a look? In fact we have also found the bug in onFailure that evaluated process also in case of `End` termination. 

I think we need to go through the various cleanup // fallback combinators and verify them and validate their defintion. 

What do you think? I was thinking its maybe a good time to foxus on either trampolined or lazy version of the Await, and maybe we will need to touch Emit as well. 

what do you think?