Fix bug #12291 Table wasn't reinited for index scan after sequential scan

Optimizer did choose "Range checked for each record" for one of the tables.
For first few loops over that table it choose sequential access, on later
stage it choose to use index. Because table was previously initialized for 
sequential access, it skips intitialization for index access, and when
server tries to retrieve data error occurs.

QUICK_RANGE_SELECT::init() changes so if file already initialized for
sequential access, it calls ha_rnd_end() and initializes file for index
access.

mysql-test/r/select.result

@@ -2943,3 +2943,20 @@ select * from t1 join t2 join t4 using (c);
 c	a	b
 1	1	1
 drop table t1, t2, t3, t4;
+create table t1(x int, y int);
+create table t2(x int, y int);
+create table t3(x int, primary key(x));
+insert into t1 values (1, 1), (2, 1), (3, 1), (4, 3), (5, 6), (6, 6);
+insert into t2 values (1, 1), (2, 1), (3, 3), (4, 6), (5, 6);
+insert into t3 values (1), (2), (3), (4), (5);
+select t1.x, t3.x from t1, t2, t3  where t1.x = t2.x and t3.x >= t1.y and t3.x <= t2.y;
+x	x
+1	1
+2	1
+3	1
+3	2
+3	3
+4	3
+4	4
+4	5
+drop table t1,t2,t3;

mysql-test/t/select.test

@@ -2523,3 +2523,15 @@ select * from t1, t2 join t3 on (t2.b = t3.b and t1.a = t3.a);
 select * from t1 join t2 join t3 join t4 on (t1.a = t4.c and t2.b = t4.c);
 select * from t1 join t2 join t4 using (c);
 drop table t1, t2, t3, t4;
+
+#
+# Bug #12291 Table wasn't reinited for index scan after sequential scan 
+#
+create table t1(x int, y int);
+create table t2(x int, y int);
+create table t3(x int, primary key(x));
+insert into t1 values (1, 1), (2, 1), (3, 1), (4, 3), (5, 6), (6, 6);
+insert into t2 values (1, 1), (2, 1), (3, 3), (4, 6), (5, 6);
+insert into t3 values (1), (2), (3), (4), (5);
+select t1.x, t3.x from t1, t2, t3  where t1.x = t2.x and t3.x >= t1.y and t3.x <= t2.y;
+drop table t1,t2,t3;

sql/opt_range.cc

@@ -750,10 +750,9 @@ int QUICK_RANGE_SELECT::init()
 {
   DBUG_ENTER("QUICK_RANGE_SELECT::init");
 
-  if (file->inited == handler::NONE)
+  if (file->inited != handler::NONE)
+    file->ha_index_or_rnd_end();
   DBUG_RETURN(error= file->ha_index_init(index));
-  error= 0;
-  DBUG_RETURN(0);
 }