tests/bitarithm_timings: Fixed hang
tests/bitarithm_timings: Fixed hang

Prevent bitarithm_lsb() from being called with 0, as it loops forever then

RIOT-OS/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,ant9000/RIOT,OTAkeys/RIOT,ant9000/RIOT,kYc0o/RIOT,x3ro/RIOT,kYc0o/RIOT,kaspar030/RIOT,toonst/RIOT,smlng/RIOT,authmillenon/RIOT,miri64/RIOT,smlng/RIOT,mtausig/RIOT,authmillenon/RIOT,aeneby/RIOT,toonst/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,aeneby/RIOT,jasonatran/RIOT,OlegHahm/RIOT,josephnoir/RIOT,ant9000/RIOT,x3ro/RIOT,toonst/RIOT,miri64/RIOT,toonst/RIOT,josephnoir/RIOT,basilfx/RIOT,basilfx/RIOT,basilfx/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,miri64/RIOT,josephnoir/RIOT,ant9000/RIOT,kaspar030/RIOT,authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,kaspar030/RIOT,authmillenon/RIOT,x3ro/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,jasonatran/RIOT,OlegHahm/RIOT,miri64/RIOT,josephnoir/RIOT,yogo1212/RIOT,OTAkeys/RIOT,mtausig/RIOT,jasonatran/RIOT,miri64/RIOT,kaspar030/RIOT,smlng/RIOT,smlng/RIOT,basilfx/RIOT,kYc0o/RIOT,authmillenon/RIOT,jasonatran/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,x3ro/RIOT,basilfx/RIOT,mtausig/RIOT,authmillenon/RIOT,kYc0o/RIOT,yogo1212/RIOT,OTAkeys/RIOT,aeneby/RIOT,OlegHahm/RIOT,toonst/RIOT,aeneby/RIOT,smlng/RIOT,yogo1212/RIOT,yogo1212/RIOT,josephnoir/RIOT,mtausig/RIOT,mtausig/RIOT,OlegHahm/RIOT,aeneby/RIOT,yogo1212/RIOT,x3ro/RIOT