#14555 Allow statistical grid cases to be used as source for grid calculator expressions

Statistics cases were filtered out of the case lists used by the grid calculator, both in the variable table and in the Select Result dialog. Statistics cases belonging to a grid ensemble were also missing from RimProject::allGridCases(), as only the source cases of the ensemble were collected. Statistics cases in a grid case group were already included.

A statistics case can be used as source only. A calculated result stored in a statistics case is interpreted as computed statistics, and would block recomputation of the statistics, so a statistics case is never assigned as destination case.

A statistics case with no computed statistics is not necessarily opened. Make sure source cases are opened before grid dimensions are validated and before result data is read.

ApplicationLibCode/ProjectDataModel/RimProject.cpp

@@ -644,10 +644,20 @@ std::vector<RimCase*> RimProject::allGridCases() const
 
             for ( RimReservoirGridEnsemble* ensemble : analysisModels->reservoirGridEnsembles.childrenByType() )
             {
+                if ( ensemble == nullptr ) continue;
+
                 for ( RimEclipseCase* acase : ensemble->cases() )
                 {
                     cases.push_back( acase );
                 }
+
+                if ( ensemble->statisticsCaseCollection() )
+                {
+                    for ( RimEclipseCase* eclipseCase : ensemble->statisticsCaseCollection()->reservoirs )
+                    {
+                        cases.push_back( eclipseCase );
+                    }
+                }
             }
 
             RimGeoMechModels* geomModels = oilField->geoMechModels();