Fix misleading error message: Clean stack rule

Summary:
Error messages in cleanstack is misleading as
it lets the user believe that there are extra
elements on stack which is incorrect if the
stack is empty.

This is a backport of core#20006

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10411