MDEV-25536 InnoDB: Failing assertion: sym_node->table != NULL in pars_retrieve_table_def

InnoDB tries to fetch the deleted doc ids for discarded
tablespace. In i_s_fts_deleted_generic_fill(), InnoDB needs
to check whether the table is discarded or not before fetching
deleted doc ids.

mysql-test/suite/innodb_fts/r/innodb_fts_misc_1.result

@@ -962,3 +962,13 @@ UPDATE t1 SET f6='cascade';
 ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t1`, CONSTRAINT `t1_ibfk_3` FOREIGN KEY (`f5`) REFERENCES `t1` (`f6`) ON UPDATE SET NULL)
 DROP TABLE t1;
 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS;
+#
+# MDEV-25536 sym_node->table != NULL in pars_retrieve_table_def
+#
+CREATE TABLE t1 (f1 TEXT,FULLTEXT (f1)) ENGINE=InnoDB;
+ALTER TABLE t1 DISCARD TABLESPACE;
+SET GLOBAL innodb_ft_aux_table='test/t1';
+SELECT * FROM information_schema.innodb_ft_deleted;
+DOC_ID
+DROP TABLE t1;
+SET GLOBAL innodb_ft_aux_table=DEFAULT;

mysql-test/suite/innodb_fts/t/innodb_fts_misc_1.test

@@ -932,3 +932,13 @@ UPDATE t1 SET f6='cascade';
 DROP TABLE t1;
 
 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS;
+
+--echo #
+--echo # MDEV-25536 sym_node->table != NULL in pars_retrieve_table_def
+--echo #
+CREATE TABLE t1 (f1 TEXT,FULLTEXT (f1)) ENGINE=InnoDB;
+ALTER TABLE t1 DISCARD TABLESPACE;
+SET GLOBAL innodb_ft_aux_table='test/t1';
+SELECT * FROM information_schema.innodb_ft_deleted;
+DROP TABLE t1;
+SET GLOBAL innodb_ft_aux_table=DEFAULT;

storage/innobase/handler/i_s.cc

@@ -2901,7 +2901,8 @@ i_s_fts_deleted_generic_fill(
 	if (!user_table) {
 		rw_lock_s_unlock(&dict_operation_lock);
 		DBUG_RETURN(0);
-	} else if (!dict_table_has_fts_index(user_table)) {
+	} else if (!dict_table_has_fts_index(user_table)
+		   || !user_table->is_readable()) {
 		dict_table_close(user_table, FALSE, FALSE);
 		rw_lock_s_unlock(&dict_operation_lock);
 		DBUG_RETURN(0);