Store reference to UnstructuredGrid in EclipseWriter

opm/core/io/eclipse/EclipseWriter.cpp

@@ -803,6 +803,7 @@ EclipseWriter::EclipseWriter (
         std::shared_ptr <EclipseGridParser> parser,
         std::shared_ptr <UnstructuredGrid> grid)
     : parser_ (parser)
+    , grid_ (grid)
     , uses_ (phaseUsageFromDeck (*parser)) {
 
     // get the base name from the name of the deck

opm/core/io/eclipse/EclipseWriter.hpp

@@ -82,6 +82,7 @@ public:
 
 private:
     std::shared_ptr <EclipseGridParser> parser_;
+    std::shared_ptr <UnstructuredGrid> grid_;
     std::string outputDir_;
     std::string baseName_;
     PhaseUsage uses_;           // active phases in the input deck