MDEV-21233 Assertion `m_extra_cache' failed in ha_partition::late_extra_cache

Incorrect assertion of EXTRA_CACHE for
HA_EXTRA_PREPARE_FOR_UPDATE. The latter is related to read cache, but
must operate without it as a noop.

Related to Bug#55458 and MDEV-20441.

mysql-test/suite/versioning/r/partition.result

@@ -605,3 +605,12 @@ Table	Op	Msg_type	Msg_text
 test.t1	check	note	Not supported for non-INTERVAL history partitions
 test.t1	check	note	The storage engine for the table doesn't support check
 drop table t1;
+#
+# MDEV-21233 Assertion `m_extra_cache' failed in ha_partition::late_extra_cache
+#
+create table t1 (id int, a varchar(8)) with system versioning partition by key (id) partitions 2;
+insert into t1 values  (1,'foo'),(2,'bar');
+create table t2 (b int);
+insert into t2 values (1),(2);
+update t1, t2 set a = 1;
+drop table t1, t2;

mysql-test/suite/versioning/t/partition.test

@@ -553,5 +553,18 @@ check table t1;
 # cleanup
 drop table t1;
 
+--echo #
+--echo # MDEV-21233 Assertion `m_extra_cache' failed in ha_partition::late_extra_cache
+--echo #
+create table t1 (id int, a varchar(8)) with system versioning partition by key (id) partitions 2;
+insert into t1 values  (1,'foo'),(2,'bar');
+
+create table t2 (b int);
+insert into t2 values (1),(2);
+
+update t1, t2 set a = 1;
+
+# cleanup
+drop table t1, t2;
 
 --source suite/versioning/common_finish.inc

sql/ha_partition.cc

@@ -9227,7 +9227,6 @@ void ha_partition::late_extra_cache(uint partition_id)
   }
   if (m_extra_prepare_for_update)
   {
-    DBUG_ASSERT(m_extra_cache);
     (void) file->extra(HA_EXTRA_PREPARE_FOR_UPDATE);
   }
   m_extra_cache_part_id= partition_id;