Emit the right message if temporary file is deleted

[pvdrz]

Describe the changes done on this pull request This PR updates visudo so it emits unable to re-open temporary file (/etc/sudoers.tmp), /etc/sudoers unchanged when sudoers.tmp is deleted while editing.

Blocked by #664

Pull Request Checklist

• [x] I have read and accepted the code of conduct for this project.
• [x] I have tested, formatted and ran clippy over my changes.
• [x] I have commented and documented my changes.
• [x] This pull request will fix parts of #657 where a proper discussion about a solution has taken place.

[github-actions[bot]]

Number of dependencies and binary size impact report

Metric	main	PR #665	Delta
Direct dependencies	3	3	-
Total dependencies	4	4	-
Binary size	979 KiB	983.1 KiB	+0.4%
Text size	571.5 KiB	574.4 KiB	+0.5%

Dependencies diff

```diff └─ sudo-rs [v0.2.0-dev.20230703] ├─ glob [v0.3.1] ├─ libc [v0.2.147] └─ log [v0.4.19] ```