do not overwrite old backup until new backup is done

src/gui_qt/main/mainwindow.py

@@ -1095,7 +1095,10 @@ class NMRMainWindow(QtWidgets.QMainWindow, Ui_BaseWindow):
     def _autosave(self):
         # TODO better separate thread may it takes some time to save
         self.status.setText('Autosave...')
-        NMRWriter(self.management.graphs, self.management.data).export(self.__backup_path)
+        success = NMRWriter(self.management.graphs, self.management.data).export(self.__backup_path.with_suffix('.nmr.0'))
+        if success:
+            self.__backup_path.with_suffix('.nmr.0').rename(self.__backup_path)
+
         self.status.setText('')
 
     def check_for_backup(self):

src/nmreval/io/sessionwriter.py

@@ -22,6 +22,11 @@ class NMRWriter:
         if isinstance(fname, str):
             fname = Path(fname)
 
+        try:
             with fname.open(mode='wb') as fh:
                 fh.write(pack('16s', b'NMREVAL' + bytes(__version__, 'utf8')))
                 dump(self._states, fh)
+            return True
+        except Exception as e:
+            print(f'Saving {fname} failed with exception {e.args}')
+            return False