fix bug I put in previous modif (used if useCubedSphereExchange and not  withSigns and without EXCH2 <- only used if implicitIntGravWave  in recently EXCH calls from do_stagger_fields_exchanges.F)
fix bug I put in previous modif (used if useCubedSphereExchange and not
 withSigns and without EXCH2 <- only used if implicitIntGravWave
 in recently EXCH calls from do_stagger_fields_exchanges.F)

altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h