MDEV-23991 fixup: Initialize the memory

Also, revert the work-around for the test that was attempted in
commit 85613a3.

This issue was caught by MemorySanitizer as well as on the
Microsoft Windows debug builds, thanks to /MD being used
starting with 10.4.

The code fix will also be applied to 10.2 because the regression
was introduced in commit afc9d00.

mysql-test/main/innodb_ext_key,off.rdiff

@@ -150,6 +150,15 @@
  Handler_read_rnd_deleted	0
  Handler_read_rnd_next	0
  explain
+@@ -209,7 +209,7 @@
+ where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000
+ or l_receiptdate='1992-07-01' and l_orderkey between 5001 and 6000;
+ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+-1	SIMPLE	lineitem	index_merge	PRIMARY,i_l_shipdate,i_l_receiptdate,i_l_orderkey,i_l_orderkey_quantity	i_l_shipdate,i_l_receiptdate	#	NULL	#	Using
++1	SIMPLE	lineitem	index_merge	PRIMARY,i_l_shipdate,i_l_receiptdate,i_l_orderkey,i_l_orderkey_quantity	i_l_shipdate,PRIMARY,i_l_receiptdate,PRIMARY	#	NULL	#	Using
+ flush status;
+ select l_orderkey, l_linenumber from lineitem 
+ where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000
 @@ -220,12 +220,12 @@
  5959	3
  show status like 'handler_read_next';

mysql-test/main/innodb_ext_key.result

@@ -204,6 +204,12 @@ Handler_read_retry	0
 Handler_read_rnd	3
 Handler_read_rnd_deleted	0
 Handler_read_rnd_next	0
+explain
+select l_orderkey, l_linenumber from lineitem 
+where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000
+or l_receiptdate='1992-07-01' and l_orderkey between 5001 and 6000;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	lineitem	index_merge	PRIMARY,i_l_shipdate,i_l_receiptdate,i_l_orderkey,i_l_orderkey_quantity	i_l_shipdate,i_l_receiptdate	#	NULL	#	Using
 flush status;
 select l_orderkey, l_linenumber from lineitem 
 where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000

mysql-test/main/innodb_ext_key.test

@@ -98,11 +98,11 @@ select l_orderkey, l_linenumber
          or l_receiptdate='1992-07-01' and l_orderkey between 5001 and 6000;
 show status like 'handler_read%';
 
-# FIXME: optimizer_switch=extended_keys=off occasionally gets wrong plan
-#explain
-#select l_orderkey, l_linenumber from lineitem
-#  where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000
-#        or l_receiptdate='1992-07-01' and l_orderkey between 5001 and 6000;
+--replace_column 7 # 9 # 10 Using
+explain
+select l_orderkey, l_linenumber from lineitem 
+  where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000
+        or l_receiptdate='1992-07-01' and l_orderkey between 5001 and 6000;
 flush status;
 select l_orderkey, l_linenumber from lineitem 
   where l_shipdate='1992-07-01' and l_orderkey between 1 and 1000

storage/innobase/dict/dict0stats.cc

@@ -2244,6 +2244,9 @@ dict_stats_update_persistent(
 	}
 
 	ut_ad(!dict_index_is_ibuf(index));
+	mutex_enter(&dict_sys.mutex);
+	dict_stats_empty_index(index, false);
+	mutex_exit(&dict_sys.mutex);
 
 	index_stats_t stats = dict_stats_analyze_index(index);