Deal with the troubles coming from bad chosen representations of k-regular sequences, where mu[0]*right != right. (This makes troubles as leading zeros of digit expansions should not influence the result.)

Depends on #21204

Component: combinatorics

Author: Daniel Krenn

Branch/Commit: u/dkrenn/k-regular-warning @ 4af416c

Issue created by migration from https://trac.sagemath.org/ticket/21343