IMPORTANT: Corrected bug in LwSrc

[arango]

In ​src:ticket:860, an update to vertical influx point sources (like river runoff) was released. However, the IF-conditional in step3d_t.F was outside of the tracer DO-loop. We need to have instead:

      IF (LwSrc(ng)) THEN
        DO itrc=1,NT(ng)
          IF (.not.((Hadvection(itrc,ng)%MPDATA).and.                   &
     &              (Vadvection(itrc,ng)%MPDATA))) THEN
            DO is=1,Nsrc(ng)
              Isrc=SOURCES(ng)%Isrc(is)
              Jsrc=SOURCES(ng)%Jsrc(is)
              IF (((Istr.le.Isrc).and.(Isrc.le.Iend+1)).and.            &
     &            ((Jstr.le.Jsrc).and.(Jsrc.le.Jend+1))) THEN
                DO k=1,N(ng)
                  cff=dt(ng)*pm(i,j)*pn(i,j)
# ifdef SPLINES_VDIFF
                  cff=cff*oHz(Isrc,Jsrc,k)
# endif
                  IF (LtracerSrc(itrc,ng)) THEN
                    cff3=SOURCES(ng)%Tsrc(is,k,itrc)
                  ELSE
                    cff3=t(Isrc,Jsrc,k,3,itrc)
                  END IF
                  t(Isrc,Jsrc,k,nnew,itrc)=t(Isrc,Jsrc,k,nnew,itrc)+    &
     &                                     cff*SOURCES(ng)%Qsrc(is,k)*  &
     &                                     cff3
                END DO
              END IF
            END DO
          END IF
        END DO
      END IF

The TLM, RPM, ADM version of step3d_t.F was also updated.

Many thanks to Chuning Wang and John Wilkin for reporting this bug.