Yup, the query will run, but the intention there is for the query optimizer to recognize the LIMIT 0 and internally reduce that query down to something that quickly returns an empty set (look for "LIMIT Query Optimization" in the MySQL documentation).

In general, when you spot an odd-looking construct in one of my SMF patches, it's likely because I estimated that the alternative way(s) of doing that thing would have led to a less compact diff. Obviously, I'm not going to favor small diffs over every other concern, but it is something that heavily factors into my decision-making (because, in turn, I believe it's something that factors into theymos' decision-making).