Returns the gym env wrapper of the given class, or None.

def get_wrapper_by_cls(env, cls):
    """Returns the gym env wrapper of the given class, or None."""
    currentenv = env
    while True:
        if isinstance(currentenv, cls):
            return currentenv
        elif isinstance(currentenv, gym.Wrapper):
            currentenv = currentenv.env
        else:
            return None