Fix the optimization of check-in [663f5dd32d9db832] that strives to avoid duplicate compuations in the GROUP BY clause so that it works even if the GROUP BY term is a subquery on the RHS of a LEFT JOIN. Problem found by dbsqlfuzz. Test cases in TH3. (tags: trunk)

Fix the optimization of check-in [663f5dd32d9db832] that strives to avoid duplicate compuations in the GROUP BY clause so that it works even if the GROUP BY term is a subquery on the RHS of a LEFT JOIN. Problem found by dbsqlfuzz. Test cases in TH3. (tags: trunk)