navigator: clarify NaN return for get_yaw_acceptance
navigator: clarify NaN return for get_yaw_acceptance

Aerotenna/Firmware,PX4/Firmware,krbeverx/Firmware,dagar/Firmware,dagar/Firmware,acfloria/Firmware,dagar/Firmware,dagar/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,dagar/Firmware,dagar/Firmware,acfloria/Firmware,Aerotenna/Firmware,PX4/Firmware,PX4/Firmware,Aerotenna/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,PX4/Firmware,PX4/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,Aerotenna/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware