Fix vcl condition --comment flag

[jedisct1]

Change summary

Fixes 2 bugs in the vcl condition update command:

• When --comment was provided, it was overwriting the condition's statement with the comment text.
• The no-arguments validation check did not include --comment

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

• N/A

Changes to Core Features:

• Have you written new tests for your core changes, as applicable?
• Have you successfully run tests with your changes locally?

User Impact

--comment updates the comment.

Are there any considerations that need to be addressed for release?

None.

[philippschulte]

LGTM. Thank you!