Clarify a comment.

storage/innobase/btr/btr0cur.c

@@ -2429,8 +2429,8 @@ btr_cur_pessimistic_update(
 	record on its page? */
 	was_first = page_cur_is_before_first(page_cursor);
 
-	/* The first parameter means that no lock checking and undo logging
-	is made in the insert */
+	/* Lock checks and undo logging were already performed by
+	btr_cur_upd_lock_and_undo(). */
 
 	err = btr_cur_pessimistic_insert(BTR_NO_UNDO_LOG_FLAG
 					 | BTR_NO_LOCKING_FLAG