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

Change-Id: I0953914a35f2a8c4caa6f75d4918e3b3366d07e8
Reviewed-on: https://gerrit.libreoffice.org/68628
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>