FIX: resolve issue on flow distances computation

This commit fix an error when flow distances are computed
on adjacent non-nested catchments

doc/source/release/0.5.0-notes.rst

@@ -92,10 +92,17 @@ Segmentation algorithm
 
 If multiple events are detected, the duration of the merged event is no longer constrained by the max duration parameter. Instead, its duration may exceed this value.
 
-``smash.generate_mesh`` segmentation fault
-******************************************
+Catchment delineation segmentation fault
+****************************************
 
 An error occured when two neighboring cells have antagonistic flow directions ``(1, 5)``, ``(2, 6)``, ``(3, 7)``, ``(4, 8)``. This should be corrected directly in the flow direction file but to avoid 
 segmentation faults when the maximum number of recursions has been reached, a check is added to the code to exit recursion in that case.
 
 See issue `#31 <https://github.com/DassHydro-dev/smash/issues/31>`__.
+
+Catchment flow distances on adjacent non-nested catchments
+**********************************************************
+
+There is a bug when calculating flow distances when two adjacent catchments are considered in the mesh but non-nested. During calculation, a flag is set around the 8 adjacent cells of each upstream cell and not on the upstream cell in particular. As a result, a gauge stuck to a cell of another catchment will not be considered as a non-nested gauge and will be filled with -99. The bug has been solved by flagging only the upstream cell and not the 8 adjacent cells.
+
+See issue `#38 <https://github.com/DassHydro-dev/smash/issues/38>`__.

smash/mesh/mw_meshing.f90

@@ -345,18 +345,18 @@ recursive subroutine distance_upstream_cells(nrow, ncol, ng, &
             row_imd = row + drow(i)
             col_imd = col + dcol(i)
 
-            do j = 1, ng
-
-                if (row_imd .eq. row_dln(j) .and. &
-                & col_imd .eq. col_dln(j)) flag(j) = 1
-
-            end do
-
             if (row_imd .gt. 0 .and. row_imd .le. nrow .and. &
             &   col_imd .gt. 0 .and. col_imd .le. ncol) then
 
                 if (flwdir(row_imd, col_imd) .eq. i) then
 
+                    do j = 1, ng
+
+                        if (row_imd .eq. row_dln(j) .and. &
+                        & col_imd .eq. col_dln(j)) flag(j) = 1
+
+                    end do
+
                     !% Avoid to compute square root if not diagonal
                     if (dcol(i) .eq. 0) then