[REVIEW 3-6][REVIEWED] Prevent crash on loading xls with pivot table (fdo#54303)

[Markus Mohrhard]

Hey Kohei,


> https://gerrit.libreoffice.org/gitweb?p=core.git;a=commitdiff;h=b4f913b5f5c48335dc80a5322b078e1d6ac2e3fe
>
> cherry-picked to 3-6 in order to fix
>
> https://bugs.freedesktop.org/show_bug.cgi?id=54303
>

Looks safe. You've my sign-off for 3-6.

Thanks,
Markus