sys/fuzzing: fix compilation with NDEBUG
sys/fuzzing: fix compilation with NDEBUG


ant9000/RIOT,jasonatran/RIOT,kaspar030/RIOT,miri64/RIOT,OlegHahm/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,miri64/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,kaspar030/RIOT,ant9000/RIOT,jasonatran/RIOT,kaspar030/RIOT,kYc0o/RIOT,ant9000/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,kYc0o/RIOT,ant9000/RIOT,ant9000/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,miri64/RIOT,jasonatran/RIOT,miri64/RIOT