MDEV-16241 Assertion `inited==RND' failed in handler::ha_rnd_end()

Discrepancy in open indexes due to overwritten `read_partitions` upon
`ha_open()` in `ha_partition::clone()`.

[Fixes tempesta-tech/mariadb#551]

mysql-test/main/partition_innodb.result

@@ -925,3 +925,14 @@ test_jfg	test_jfg11
 test_jfg	test_jfg12#P#p1000
 test_jfg	test_jfg12#P#pmax
 DROP DATABASE test_jfg;
+#
+# MDEV-16241 Assertion `inited==RND' failed in handler::ha_rnd_end()
+#
+CREATE TABLE t1 (pk INT PRIMARY KEY, x INT, y INT, z INT, KEY (x), KEY (y, z))
+WITH SYSTEM VERSIONING
+PARTITION BY SYSTEM_TIME (PARTITION p1 HISTORY, PARTITION pn CURRENT);
+INSERT INTO t1 VALUES (1, 7, 8, 9), (2, NULL, NULL, NULL), (3, NULL, NULL, NULL);
+SELECT COUNT(*) FROM t1 WHERE x IS NULL AND y IS NULL AND z IS NULL;
+COUNT(*)
+2
+DROP TABLE t1;

mysql-test/main/partition_innodb.test

@@ -1015,3 +1015,13 @@ SELECT database_name, table_name FROM mysql.innodb_table_stats WHERE
 database_name = 'test_jfg';
 
 DROP DATABASE test_jfg;
+
+--echo #
+--echo # MDEV-16241 Assertion `inited==RND' failed in handler::ha_rnd_end()
+--echo #
+CREATE TABLE t1 (pk INT PRIMARY KEY, x INT, y INT, z INT, KEY (x), KEY (y, z))
+WITH SYSTEM VERSIONING
+PARTITION BY SYSTEM_TIME (PARTITION p1 HISTORY, PARTITION pn CURRENT);
+INSERT INTO t1 VALUES (1, 7, 8, 9), (2, NULL, NULL, NULL), (3, NULL, NULL, NULL);
+SELECT COUNT(*) FROM t1 WHERE x IS NULL AND y IS NULL AND z IS NULL;
+DROP TABLE t1;

sql/ha_partition.cc

@@ -3516,7 +3516,8 @@ int ha_partition::open(const char *name, int mode, uint test_if_locked)
   if (init_partition_bitmaps())
     goto err_alloc;
 
-  if (unlikely((error=
+  if (!MY_TEST(m_is_clone_of) &&
+      unlikely((error=
                 m_part_info->set_partition_bitmaps(m_partitions_to_open))))
     goto err_alloc;