...which has no effect on the result, but silences benign Clang
-fsanitize=implicit-signed-integer-truncation warnings

Change-Id: Ic2cf38466f12462d67ceb6268d5197e13cc6143a
Reviewed-on: https://gerrit.libreoffice.org/68627
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>