Don't fail the samefile check if second file didn't exist

If the backup file didn't exist but the original did, then apparently they are not the same file so the copy should be allowed.

cura/Backups/Backup.py

@@ -50,7 +50,7 @@ class Backup:
             preferences_file_name = self._application.getApplicationName()
             preferences_file = Resources.getPath(Resources.Preferences, "{}.cfg".format(preferences_file_name))
             backup_preferences_file = os.path.join(version_data_dir, "{}.cfg".format(preferences_file_name))
-            if not os.path.samefile(preferences_file, backup_preferences_file):
+            if os.path.exists(preferences_file) and (not os.path.exists(backup_preferences_file) or not os.path.samefile(preferences_file, backup_preferences_file)):
                 Logger.log("d", "Copying preferences file from %s to %s", preferences_file, backup_preferences_file)
                 shutil.copyfile(preferences_file, backup_preferences_file)