MDEV-24781 Assertion `mode == 16 || mode == 12 || fix_block->page.status != buf_page_t::FREED' failed in buf_page_get_low

This is caused by commit 3cef4f8f
(MDEV-515). dict_table_t::clear() frees all the blob during
rollback of bulk insert.But online log tries to read the
freed blob while applying the log. It can be fixed if we
truncate the online log during rollback of bulk insert operation.