Q:

When reviewing, what to do when previous reviewer has already posted a comment?

On a recent review of a first post the previous reviewer, a moderator, had already posted a comment that covered the issue. 
The post was asked on the wrong SE site, but their comment covered this.
I decided to flag for moderator intervention because the 'No action necessary' pop-up for this action says "This question seems to be valid", which it isn't on the site it was posted on. But, a moderator was already aware as they commented so is flagging it just making work for others, or is this correct action?
I have done some looking around on the Metas but can't find an answer to this I don't think?
What are the review queues, and how do they work?
How does the new user question review process work?

A:

If you don't want to flag it, you can always upvote the previous reviewer's comment and then click on "I'm done".

