Bug if no lateral diffusion for passive tracers but isopycnal mixing for active tracers

If one choose not to have lateral diffusion for passive tracers (i.e. ln_trcldf_OFF=T), but one has isopycnal diffusion for active tracers (i.e. l_ldfslp=T), there will be a wrong vertical diffusivity in tra_zdf_imp:

           ELSE                                               ! use avs for salinty or passive tracers
              !                                                                          

              IF( l_ldfslp ) THEN            ! use avs + isoneutral diffusion contribution
                 IF( ln_traldf_msc  ) THEN        ! MSC iso-neutral operator
                    DO_2Dik( 0, 0,   2, jpk, 1 )
                       zwt(ji,jk) = avs(ji,jj,jk) + akz(ji,jj,jk)
                    END_2D
                 ELSE                             ! standard or triad iso-neutral operator
                    DO_2Dik( 0, 0,   2, jpk, 1 )
                       zwt(ji,jk) = avs(ji,jj,jk) + ah_wslp2(ji,jj,jk)
                    END_2D
                 ENDIF
              ELSE                          !
                 DO_2Dik( 0, 0,   2, jpk, 1 )
                    zwt(ji,jk) = avs(ji,jj,jk)
                 END_2D
              ENDIF
           ENDIF

One should only consider avs in zwt that case.