added missing const specifier for gridview get-method in ProblemStat

src/amdis/ProblemStat.hpp

@@ -276,7 +276,7 @@ namespace AMDiS
     Grid const& grid() const { return *grid_; }
 
     /// Return the gridView of the leaf-level
-    GridView const& gridView() { return globalBasis_->gridView(); }
+    GridView const& gridView() const { return globalBasis_->gridView(); }
 
     /// Return the \ref globalBasis_
     GlobalBasis&       globalBasis()       { return *globalBasis_; }