nrf802154: don't call memcpy if iolist->iol_len==0
nrf802154: don't call memcpy if iolist->iol_len==0

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