Backup file scheme not working properly with single file name on command line in 0.26.10

Unfortunately the backup file scheme on "Save" isn't working properly.

Sometimes an error happens

```
Warning: Could not create backup file: unable to rename original file 'x.gds' to backup file
```

This happens specifically when a single file is specified on the command line.

The file is saved but without the backup feature.

Matthias

