amp2response: Better messaging for erroneous b=0 lmax
amp2response: Better messaging for erroneous b=0 lmax

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3