pamhyr: Add periodic backup.

src/Model/Study.py

@@ -104,9 +104,13 @@ class Study(SQLModel):
                 logger.error(e)
 
         fname = fname + "." + str(self._old_save_id)
-        filename = os.path.join(fdir, "_PAMHYR_", "__old__", fname)
-        shutil.copy(self.filename, filename)
-        self._old_save_id += 1
+        if os.path.exists(self.filename) and ".backup" not in self.filename:
+            filename = os.path.join(fdir, "_PAMHYR_", "__old__", fname)
+            logger.debug(f"Backup previous version copy: {filename}")
+            shutil.copy(self.filename, filename)
+            self._old_save_id += 1
+        else:
+            self._init_db_file(self.filename, is_new=True)
 
         # Save
         self.last_save_date = datetime.now()
@@ -128,6 +132,16 @@ class Study(SQLModel):
 
     @filename.setter
     def filename(self, filename):
+        if filename is None:
+            self._filename = None
+            self.status.modified()
+            return
+
+        if self._filename is not None and self._filename != "":
+            self._filename = str(filename)
+            self.status.modified()
+            return
+
         self._filename = str(filename)
         self._init_db_file(filename, is_new=True)
         self.status.modified()