No KeyErrror raised when it should for FiniteWord_callable

<div id="comment:0"></div>


```
Le 10-02-23, Paul Zimmermann a écrit :

sage: def f(n):
   return n^2

sage: w = Word(f,length=23)

sage: w[24]
576

Paul
```

CC:  @sagetrac-abmasse

Component: **combinatorics**

Author: **Sébastien Labbé**

Reviewer: **Alexandre Blondin Massé**

Merged: **sage-4.7.alpha3**

_Issue created by migration from https://trac.sagemath.org/ticket/8673_

