sfx2: SfxObjectShell should not trust any signature on repaired package

sfx2: SfxObjectShell should not trust any signature on repaired package

[ELTS]
cast pointer like with similar code in context

Change-Id: I0317f80989e9dabd23e88e3caab26ede3fb5bd56
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/169883
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>
(cherry picked from commit 8b333575ee680664fa3d83249ccec90881754ad7)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/169930
Reviewed-by: Caolán McNamara <caolan.mcnamara@collabora.com>
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/171910
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Gbp-Pq: Name do-not-trust-any-signature-on-repaired-package.diff