[LyX/master] Prevent division by zero

[Jürgen Spitzmüller]

Am Samstag, dem 15.06.2024 um 12:50 +0000 schrieb Juergen Spitzmueller:
> commit 0fc8ee5ace22c11175cb93f5b6f7310cc4d646c1
> Author: Juergen Spitzmueller <spitz at lyx.org>
> Date:   Sat Jun 15 14:48:37 2024 +0200
> 
>     Prevent division by zero
>     
>     Fixes crash reported at
>     https://marc.info/?l=lyx-users&m=171842978728676

Candidate for 2.4.1.

-- 
Jürgen