LP:878769 - Valgrind warning/crash in MRR with join_cache_level=8

The test case below produces the following warning:

==16327== Conditional jump or move depends on uninitialised value(s)
==16327== at 0x827B853: key_restore(unsigned char*, unsigned char*, st_key*, unsigned int) (key.cc:191)
==16327== by 0x84BCF38: Mrr_ordered_index_reader::resume_read() (multi_range_read.cc:462)
==16327== by 0x84BD5F2: Mrr_ordered_rndpos_reader::refill_from_index_reader() (multi_range_read.cc:625)
==16327== by 0x84BD45E: Mrr_ordered_rndpos_reader::refill_buffer(bool) (multi_range_read.cc:584)
==16327== by 0x84BDFFC: DsMrr_impl::dsmrr_init(handler*, st_range_seq_if*, void*, unsigned int, unsigned int, st_handler_buffer*) (multi_range_read.cc:920)
==16327== by 0x869B3BF: ha_innobase::multi_range_read_init(st_range_seq_if*, void*, unsigned int, unsigned int, st_handler_buffer*) (ha_innodb.cc:12256)
==16327== by 0x82F5325: JOIN_TAB_SCAN_MRR::open() (sql_join_cache.cc:3814)
==16327== by 0x82F3279: JOIN_CACHE::join_matching_records(bool) (sql_join_cache.cc:2208)
==16327== by 0x82F2E72: JOIN_CACHE::join_records(bool) (sql_join_cache.cc:2045)
==16327== by 0x833D787: sub_select_cache(JOIN*, st_join_table*, bool) (sql_select.cc:14901)
==16327== by 0x833D99F: sub_select(JOIN*, st_join_table*, bool) (sql_select.cc:15063)
==16327== by 0x833D48E: do_select(JOIN*, List<Item>, st_table, Procedure*) (sql_select.cc:14785)
==16327== by 0x83203A2: JOIN::exec() (sql_select.cc:2239)
==16327== by 0x8322529: mysql_select(THD*, Item**, TABLE_LIST, unsigned int, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, un
signed long long, select_result*, st_select_lex_unit*, st_select_lex*) (sql_select.cc:2900)
==16327== by 0x831A2FA: handle_select(THD*, st_lex*, select_result*, unsigned long) (sql_select.cc:283)
==16327== by 0x82B4A87: execute_sqlcom_select(THD*, TABLE_LIST*) (sql_parse.cc:5112)

test case (further simplification was not possible for sporadic crashes):

--source include/have_innodb.inc
set session optimizer_switch='derived_with_keys=ON,index_condition_pushdown=ON,mrr=ON,join_cache_hashed=ON,mrr_sort_keys=ON';
set session join_cache_level=8;

DROP TABLE IF EXISTS t1;
CREATE TABLE t1 ( col_int_key int(11), col_time_key time, col_varchar_key varchar(1), KEY (col_int_key), KEY (col_varchar_key,col_int_key)) ENGINE=InnoDB;
INSERT IGNORE INTO t1 VALUES (7,'10:19:31','d'),(1,'14:40:36','r'),(7,'04:37:47','f'),(9,'19:34:06','y'),(2,'00:00:00','m'),(4,'00:13:25','q'),(0,'03:47:16',NULL),(4,'01:41:48','d'),(8,'00:00:00','g'),(NULL,'22:32:04','x'),(NULL,'16:44:14','f'),(0,'17:38:37','p'),(NULL,'08:46:48','j'),(8,'14:11:27','c');

DROP TABLE IF EXISTS t2;
CREATE TABLE t2 ( col_int_nokey int(11), col_int_key int(11), col_datetime_key datetime, col_datetime_nokey datetime, col_varchar_key varchar(1), col_varchar_nokey varchar(1), KEY (col_int_key), KEY (col_varchar_key,col_int_key)) ;
INSERT IGNORE INTO t2 VALUES (150,62,'2008-01-03 10:33:32','2008-01-03 10:33:32','v','v'),(2,1,'2007-10-09 19:53:04','2007-10-09 19:53:04',NULL,NULL),(5,0,'2001-11-08 21:02:12','2001-11-08 21:02:12','x','x'),(3,7,'2003-04-01 00:00','2003-04-01 00:00','i','i'),(1,7,'1900-01-01 00:00','1900-01-01 00:00:00','e','e'),(NULL,7,'2005-04-04 01:21','2005-04-04 01:21','s','s'),(2,1,'1900-01-01 00:00','1900-01-01 00:00','j','j'),(8,0,'2004-04-28 21:44','2004-04-28 21:44','a','a'),(6,8,'2001-04-18 00:00','2001-04-18 00:00:00','y','y'),(8,1,'2008-12-18 19:39:55','2008-12-18 19:39:55',NULL,NULL),(3,1,'2000-08-01 12:19:39','2000-08-01 12:19:39','r','r'),(3,9,'2004-09-25 21:29:06','2004-09-25 21:29:06','v','v');

CREATE OR REPLACE ALGORITHM=MERGE VIEW v2 AS SELECT * FROM t2;

SELECT t1.col_time_key, t1.col_varchar_key
FROM
( v2 STRAIGHT_JOIN t1 ON
(t1.col_int_key = v2.col_int_key )
)
GROUP BY 1 , 2 ;

bzr version-info
revision-id: <email address hidden>
date: 2011-10-19 21:01:42 +0200
build-date: 2011-10-20 13:50:14 +0300
revno: 3242
branch-nick: maria-5.3

full optimizer switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,index_condition_
pushdown=on,derived_merge=off,derived_with_keys=on,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=on,
partial_match_table_scan=on,subquery_cache=on,mrr=on,mrr_cost_based=off,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremen
tal=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on