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.

Author: D. Richard Hipp

src/select.c

@@ -8498,6 +8498,11 @@ int sqlite3Select(
         if( iOrderByCol ){
           Expr *pX = p->pEList->a[iOrderByCol-1].pExpr;
           Expr *pBase = sqlite3ExprSkipCollateAndLikely(pX);
+          if( ALWAYS(pBase!=0)
+           && pBase->op==TK_IF_NULL_ROW
+          ){
+            pBase = pX = pBase->pLeft;
+          }
           if( ALWAYS(pBase!=0)
            && pBase->op!=TK_AGG_COLUMN
            && pBase->op!=TK_REGISTER