Fixed bug #20519.

The bug was due to a loss happened during a refactoring made
on May 30 2005 that modified the function JOIN::reinit.
As a result of it for any subquery the value of offset_limit_cnt
was not restored for the following executions. Yet the first 
execution of the subquery made it equal to 0.
The fix restores this value in the function JOIN::reinit.  


mysql-test/r/subselect.result:
  Added a test case fir bug #20519.
mysql-test/t/subselect.test:
  Added a test case fir bug #20519.

mysql-test/r/subselect.result

@@ -3238,3 +3238,48 @@ i
 10000000000000000000
 DROP TABLE t1;
 DROP TABLE t2;
+CREATE TABLE t1 (
+id bigint(20) unsigned NOT NULL auto_increment,
+name varchar(255) NOT NULL,
+PRIMARY KEY  (id)
+);
+INSERT INTO t1 VALUES
+(1, 'Balazs'), (2, 'Joe'), (3, 'Frank');
+CREATE TABLE t2 (
+id bigint(20) unsigned NOT NULL auto_increment,
+mid bigint(20) unsigned NOT NULL,
+date date NOT NULL,
+PRIMARY KEY  (id)
+);
+INSERT INTO t2 VALUES 
+(1, 1, '2006-03-30'), (2, 2, '2006-04-06'), (3, 3, '2006-04-13'),
+(4, 2, '2006-04-20'), (5, 1, '2006-05-01');
+SELECT *,
+(SELECT date FROM t2 WHERE mid = t1.id
+ORDER BY date DESC LIMIT 0, 1) AS date_last,
+(SELECT date FROM t2 WHERE mid = t1.id
+ORDER BY date DESC LIMIT 3, 1) AS date_next_to_last
+FROM t1;
+id	name	date_last	date_next_to_last
+1	Balazs	2006-05-01	NULL
+2	Joe	2006-04-20	NULL
+3	Frank	2006-04-13	NULL
+SELECT *,
+(SELECT COUNT(*) FROM t2 WHERE mid = t1.id
+ORDER BY date DESC LIMIT 1, 1) AS date_count
+FROM t1;
+id	name	date_count
+1	Balazs	NULL
+2	Joe	NULL
+3	Frank	NULL
+SELECT *,
+(SELECT date FROM t2 WHERE mid = t1.id
+ORDER BY date DESC LIMIT 0, 1) AS date_last,
+(SELECT date FROM t2 WHERE mid = t1.id
+ORDER BY date DESC LIMIT 1, 1) AS date_next_to_last
+FROM t1;
+id	name	date_last	date_next_to_last
+1	Balazs	2006-05-01	2006-03-30
+2	Joe	2006-04-20	2006-04-06
+3	Frank	2006-04-13	NULL
+DROP TABLE t1,t2;

mysql-test/t/subselect.test

@@ -2161,3 +2161,43 @@ SELECT t1.i FROM t1 WHERE t1.i = CAST((SELECT MAX(i) FROM t2) AS UNSIGNED);
 
 DROP TABLE t1;
 DROP TABLE t2;
+
+# 
+# Bug#20519: subselect with LIMIT M, N
+#
+
+CREATE TABLE t1 (
+  id bigint(20) unsigned NOT NULL auto_increment,
+  name varchar(255) NOT NULL,
+  PRIMARY KEY  (id)
+);
+INSERT INTO t1 VALUES
+  (1, 'Balazs'), (2, 'Joe'), (3, 'Frank');
+
+CREATE TABLE t2 (
+  id bigint(20) unsigned NOT NULL auto_increment,
+  mid bigint(20) unsigned NOT NULL,
+  date date NOT NULL,
+  PRIMARY KEY  (id)
+);
+INSERT INTO t2 VALUES 
+  (1, 1, '2006-03-30'), (2, 2, '2006-04-06'), (3, 3, '2006-04-13'),
+  (4, 2, '2006-04-20'), (5, 1, '2006-05-01');
+
+SELECT *,
+      (SELECT date FROM t2 WHERE mid = t1.id
+         ORDER BY date DESC LIMIT 0, 1) AS date_last,
+      (SELECT date FROM t2 WHERE mid = t1.id
+         ORDER BY date DESC LIMIT 3, 1) AS date_next_to_last
+  FROM t1;
+SELECT *,
+      (SELECT COUNT(*) FROM t2 WHERE mid = t1.id
+         ORDER BY date DESC LIMIT 1, 1) AS date_count
+  FROM t1;
+SELECT *,
+      (SELECT date FROM t2 WHERE mid = t1.id
+         ORDER BY date DESC LIMIT 0, 1) AS date_last,
+      (SELECT date FROM t2 WHERE mid = t1.id
+         ORDER BY date DESC LIMIT 1, 1) AS date_next_to_last
+  FROM t1;
+DROP TABLE t1,t2;

sql/sql_select.cc

@@ -1209,6 +1209,11 @@ int
 JOIN::reinit()
 {
   DBUG_ENTER("JOIN::reinit");
+
+  unit->offset_limit_cnt= (ha_rows)(select_lex->offset_limit ?
+                                    select_lex->offset_limit->val_uint() :
+                                    ULL(0));
+
   first_record= 0;
 
   if (exec_tmp_table1)