I came across a couple of places in the planner that are checking for nonempty havingQual; but since these bits run after const-simplification of the HAVING clause, that produces the wrong answer for a constant-true HAVING clause (which'll be folded to empty). Correct code is to check root->hasHavingQual instead.
+1. root->hasHavingQual is set before we do any expression preprocessing. It should be the right one to check with.
