BUG#20852: Using update with full table scan causes mysqld to enter an eternal loop

mysql-test/r/partition_innodb.result

@@ -107,3 +107,14 @@ select * from t1 where id = 'aaa';
 id
 aaa
 drop table t1;
+create table t1 (a int, b int, primary key (b,a))
+engine = innodb
+partition by hash (a);
+insert into t1 values (0, 0);
+insert into t1 values (1, 0);
+update t1 set b = b + 1 where a = 1;
+select * from t1;
+a	b
+0	0
+1	1
+drop table t1;

mysql-test/t/partition_innodb.test

@@ -78,3 +78,16 @@ select * from t1 where id = 'a';
 select * from t1 where id = 'aa';
 select * from t1 where id = 'aaa';
 drop table t1;
+
+#
+# Bug #20852 Partitions: Crash if hash innodb, composite primary key
+#
+create table t1 (a int, b int, primary key (b,a))
+engine = innodb
+partition by hash (a);
+insert into t1 values (0, 0);
+insert into t1 values (1, 0);
+update t1 set b = b + 1 where a = 1;
+select * from t1;
+drop table t1;
+

sql/ha_partition.cc

@@ -2229,7 +2229,8 @@ int ha_partition::open(const char *name, int mode, uint test_if_locked)
   m_table_flags&= ~(HA_CAN_GEOMETRY | HA_CAN_FULLTEXT | HA_DUPLICATE_POS |
                     HA_CAN_SQL_HANDLER | HA_CAN_INSERT_DELAYED);
   m_table_flags|= HA_FILE_BASED | HA_REC_NOT_IN_SEQ;
-
+  key_used_on_scan= m_file[0]->key_used_on_scan;
+  implicit_emptied= m_file[0]->implicit_emptied;
   /*
     Add 2 bytes for partition id in position ref length.
     ref_length=max_in_all_partitions(ref_length) + PARTITION_BYTES_IN_POS