Failures due to missingg credentials generate incorrect exit code

[mprasil]

I've ran rustic without password by mistake and it failed:

# rustic backup /some/path
[INFO] using config /etc/rustic/rustic.toml
error: No password given. Please use one of the --password-* options.

However exit code was 0:

# echo $?
0

Same for missing repository credentials without anonymous access. I don't think this is correct behavior as it could lead to backup scripts failing silently.

[simonsan]

This is a duplicate, please make sure to search the issues before opening a new one, or start a new discussion.

CC: #927