Minor HDF adjustments (#7577)

* #7575 Summary HDF : Do not import summary if no UNSRMY file is found
* #7575 Summary HDF : Add optional check on time stamp of h5 file
* Use std::filesystem to check file access
* Do not keep h5 file open

ApplicationLibCode/ProjectDataModelCommands/RimcProject.h

@@ -39,6 +39,7 @@ public:
     caf::PdmObjectHandle*            execute() override;
     bool                             resultIsPersistent() const override;
     std::unique_ptr<PdmObjectHandle> defaultResult() const override;
+    bool                             isNullptrValidResult() const override;
 
 private:
     caf::PdmField<QString> m_fileName;