...so standard libraries in debug mode can catch out-of-bounds element acces

Change-Id: I519795f5fcb51f243312e5d0247998eff6ceb151
Reviewed-on: https://gerrit.libreoffice.org/51008Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>