MDEV-31523 Using two temporary tables in OPTIMIZE TABLE lead to crash

Fixed typo in mysql_admin_table which cused call of
close_unused_temporary_table_instances alwas for the first table
instead of the current table.

Added ASSERT that close_unused_temporary_table_instances should not
remove all instances of user created temporary table.

mysql-test/main/temp_table.result

@@ -602,3 +602,19 @@ DROP TEMPORARY TABLE t1;
 #
 # End of 10.2 tests
 #
+#
+# MDEV-31523: Using two temporary tables in OPTIMIZE TABLE lead to crash
+#
+CREATE TEMPORARY TABLE t1 (c INT) ENGINE=MyISAM;
+CREATE TEMPORARY TABLE t2 (c INT) ENGINE=MyISAM;
+optimize TABLE t1,t2;
+Table	Op	Msg_type	Msg_text
+test.t1	optimize	status	Table is already up to date
+test.t2	optimize	status	Table is already up to date
+SHOW TABLES;
+Tables_in_test
+# in 11.2 and above here should be listed above used temporary tables
+DROP TEMPORARY TABLE t1, t2;
+#
+# End of 10.4 tests
+#

mysql-test/main/temp_table.test

@@ -661,3 +661,19 @@ DROP TEMPORARY TABLE t1;
 --echo #
 --echo # End of 10.2 tests
 --echo #
+
+--echo #
+--echo # MDEV-31523: Using two temporary tables in OPTIMIZE TABLE lead to crash
+--echo #
+
+CREATE TEMPORARY TABLE t1 (c INT) ENGINE=MyISAM;
+CREATE TEMPORARY TABLE t2 (c INT) ENGINE=MyISAM;
+optimize TABLE t1,t2;
+SHOW TABLES;
+--echo # in 11.2 and above here should be listed above used temporary tables
+
+DROP TEMPORARY TABLE t1, t2;
+
+--echo #
+--echo # End of 10.4 tests
+--echo #

sql/sql_admin.cc

@@ -776,7 +776,7 @@ static bool mysql_admin_table(THD* thd, TABLE_LIST* tables,
     if (lock_type == TL_WRITE && table->mdl_request.type > MDL_SHARED_WRITE)
     {
       if (table->table->s->tmp_table)
-        thd->close_unused_temporary_table_instances(tables);
+        thd->close_unused_temporary_table_instances(table);
       else
       {
         if (wait_while_table_is_used(thd, table->table, HA_EXTRA_NOT_USED))

sql/temporary_tables.cc

@@ -1577,6 +1577,11 @@ void THD::close_unused_temporary_table_instances(const TABLE_LIST *tl)
        {
          /* Note: removing current list element doesn't invalidate iterator. */
          share->all_tmp_tables.remove(table);
+         /*
+           At least one instance should be left (guaratead by calling this
+           function for table which is opened and the table is under processing)
+         */
+         DBUG_ASSERT(share->all_tmp_tables.front());
          free_temporary_table(table);
        }
      }