cmd/archive: additionally test for non-existence of file named -

[roobre]

What?

A follow-up to #3797, which I didn't want to push over as it already has approvals.

Why?

Additionally to check for non-existence of archive.tar, also check for non-existence of a file named -, which could happen if the special case of - = stdout is mishandled.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

#3797

[codebien]

As archive.tar is the default value, it makes sense to check that it doesn't exist. Maybe, we can check both, as they are the obvious catch in case of bugs.

[roobre]

@codebien Done!

The base branch was changed.