Joining to chains loses link_error of least chain

[atn18]

celery/celery/canvas.py

Lines 408 to 414 in cbbf481

	elif isinstance(other, _chain):
	# chain | chain -> chain
	sig = self.clone()
	if isinstance(sig.tasks, tuple):
	sig.tasks = list(sig.tasks)
	sig.tasks.extend(other.tasks)
	return sig

Should be something like

    link_error_sigs = other._with_list_option('link_error')
    sig.tasks.extend(
        reduce(
            lambda t, s: t.on_error(s), link_error_sigs, t.clone())
        for t in other.tasks)