[vtk][fix] Fix the runtime size checks to check actual vector size

dumux/io/vtkoutputmodule.hh

@@ -306,9 +306,9 @@ public:
         // also register additional (non-standardized) user fields
         for (std::size_t i = 0; i < scalarFields_.size(); ++i)
         {
-            if (scalarFields_[i].second.size() == std::size_t(problem_.gridView().size(0)))
+            if (scalarFields_[i].first.size() == std::size_t(problem_.gridView().size(0)))
                 sequenceWriter_.addCellData(scalarFields_[i].first, scalarFields_[i].second);
-            else if (scalarFields_[i].second.size() == std::size_t(problem_.gridView().size(dim)))
+            else if (scalarFields_[i].first.size() == std::size_t(problem_.gridView().size(dim)))
                 sequenceWriter_.addVertexData(scalarFields_[i].first, scalarFields_[i].second);
             else
                 DUNE_THROW(Dune::RangeError, "Cannot add wrongly sized vtk scalar field!");
@@ -316,14 +316,14 @@ public:
 
         for (std::size_t i = 0; i < vectorFields_.size(); ++i)
         {
-            if (scalarFields_[i].second.size() == std::size_t(problem_.gridView().size(0)))
+            if (scalarFields_[i].first.size() == std::size_t(problem_.gridView().size(0)))
             {
                 using NestedFunction = VtkNestedFunction<GridView, ElementMapper, std::vector<GlobalPosition>>;
                 sequenceWriter_.addCellData(std::make_shared<NestedFunction>(vectorFields_[i].second,
                                                                              problem_.gridView(), problem_.elementMapper(),
                                                                              vectorFields_[i].first, 0, dimWorld));
             }
-            else if (scalarFields_[i].second.size() == std::size_t(problem_.gridView().size(dim)))
+            else if (scalarFields_[i].first.size() == std::size_t(problem_.gridView().size(dim)))
             {
                 using NestedFunction = VtkNestedFunction<GridView, VertexMapper, std::vector<GlobalPosition>>;
                 sequenceWriter_.addVertexData(std::make_shared<NestedFunction>(vectorFields_[i].second,