A kind person resolved an issue by a throwaway one-liner in a comment instead of an answer. Bearing in mind that I cannot seem to vote on their comment, how do I:
Please resist the urge only to comment in response to this!
In general, you can tell the commenter to add their comment as an answer, and that you'll accept it. Not many folks would turn down the easy rep.
In this case, however, I would tend to agree with the others: it is not a valuable question, because it is a fairly trivial error, and the "solution" is unlikely to help future readers.
Aside from telling the commenter to post something as an answer, if they don't actually do that you can always answer your own question and credit them in it! If you don't want to reap karma from it (if you feel it's unearned) you can always make your answer a community wiki answer.
too localized.