MDEV-24693 LeakSanitizer: detected memory leaks in mem_heap_create_block_func / fts_optimize_create_msg

- This issue is caused by the commit bf1f9b59
(MDEV-24638). Delay the creation of SYNC message in
fts_optimize_request_sync_table. So that InnoDB can avoid creating
the message if the table already has SYNC message in fts_optimize_wq queue