Flip signs in Richards FV upwinding queries

dune/dorie/model/richards/local_operator_FV.hh

@@ -173,7 +173,8 @@ public:
 
       // Upwinding conductivity factor
       RangeU cond_upwind_factor(0.0);
-      if (dudn < 0.0) {
+      // NOTE: Sign seems inverted due to definition of 'water_flux_n' below.
+      if (dudn > 0.0) {
         // inward flux
         cond_upwind_factor = cond_o / cond_sat_o;
       }
@@ -188,7 +189,7 @@ public:
     else // RichardsFVUpwinding::fullUpwind
     {
       // No average: Use upwind conductivity
-      if (dudn < 0.0) {
+      if (dudn > 0.0) {
         // inward flux
         cond_f = cond_o;
       }