MDEV-17201 dropped anchor rows with non-null recursion query

The function st_select_lex_unit::exec_recursive() missed resetting of
select_limit_cnt and offset_limit_cnt before execution of union parts.
As a result recursive CTEs specified by UNIONs whose SELECTs contained
LIMIT/OFFSET could return wrong sets of records.

mysql-test/t/cte_recursive.test

@@ -2390,3 +2390,53 @@ eval $q3;
 
 drop procedure p;
 drop table t1,t2;
+
+--echo #
+--echo # MDEV-17201: recursive part with LIMIT
+--echo #
+
+CREATE TABLE purchases (
+  id int unsigned NOT NULL AUTO_INCREMENT,
+  pdate date NOT NULL,
+  quantity int unsigned NOT NULL,
+  p_id int unsigned NOT NULL,
+  PRIMARY KEY (id)
+);
+INSERT INTO purchases(pdate, quantity, p_id) VALUES
+  ('2014-11-01',5 ,1),('2014-11-03', 3 ,1),
+  ('2014-11-01',2 ,2),('2014-11-03', 4 ,2);
+
+CREATE TABLE expired (
+  edate date NOT NULL,
+  quantity int unsigned NOT NULL,
+  p_id int unsigned NOT NULL,
+  PRIMARY KEY (edate,p_id)
+);
+
+INSERT INTO expired VALUES ('2014-11-12', 5 ,1),('2014-11-08', 1 ,2);
+
+WITH RECURSIVE expired_map AS (
+   SELECT edate AS expired_date,
+          CAST(NULL AS date) AS purchase_date,
+          0 AS quantity,
+          e.p_id,
+          (SELECT MAX(id)+1 FROM purchases p
+             WHERE pdate <= edate AND p.p_id =p_id) AS purchase_processed,
+          quantity AS unresolved
+   FROM expired e
+   UNION
+   ( SELECT expired_date,
+            pdate,
+            IF(p.quantity < m.unresolved, p.quantity, m.unresolved),
+            p.p_id,
+            p.id,
+            IF(p.quantity < m.unresolved, m.unresolved - p.quantity, 0)
+     FROM purchases p JOIN expired_map m ON p.p_id = m.p_id
+     WHERE p.id < m.purchase_processed AND m.unresolved > 0
+     ORDER BY p.id DESC
+     LIMIT 1
+   )
+)
+SELECT  * FROM expired_map;
+
+DROP TABLE purchases, expired;