bug#51012: 29.0.50; Problems with emojis and vertical-motion

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Mon, 04 Oct 2021 18:43:53 +0200
> Cc: 51012@debbugs.gnu.org
> 
> This fixes it for me:
> 
> diff --git a/src/font.c b/src/font.c
> index 82a1dffc01..83f0f8296a 100644
> --- a/src/font.c
> +++ b/src/font.c
> @@ -3918,7 +3918,7 @@ font_range (ptrdiff_t pos, ptrdiff_t pos_byte, 
> ptrdiff_t *limit,
>           val = XCAR (val);
>         else if (VECTORP (val))
>           val = AREF (val, 0);
> -       font_object = font_for_char (face, XFIXNAT (val), pos - 1, string);
> +       font_object = font_for_char (face, XFIXNAT (val), pos, string);
>       }
>      }

Sounds obvious to me.  Why was there a minus there in the first place?
some remnant of debugging or the previous version?