fdo#76663: Let's not skip the first element of a matrix in PRODUCT.

(cherry picked from commit 4158d8843d50d50e9830c8dc24af8722de77f4af)

Conflicts:
	sc/source/core/tool/interpr6.cxx

Backported.

Change-Id: I00683ce64fea58a80cd7137384e8f30464c44e9f
Reviewed-on: https://gerrit.libreoffice.org/9159
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>
(cherry picked from commit b3d3c64a83c510a5c9aacf517eee8ca697e21d8f)
Reviewed-on: https://gerrit.libreoffice.org/9160
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: David Tardon <dtardon@redhat.com>