Scenario: Add delete scenario command and use undo command.

src/Model/Tools/PamhyrDB.py

@@ -195,6 +195,9 @@ class SQLSubModel(PamhyrID):
         Returns:
             Nothing
         """
+        if self._status is None:
+            return
+
         self._owner_scenario = self._status.scenario_id
         self._status.modified()