IF: Fix SIGSEGV when create_and_send_vote_msg processes its own vote

[linh2931]

SIGSEGV happened frequently in IF Boost unittests and occasionally in Integration tests. Thanks to @spoonincode, a back trace was retrieved from CICD (the problem did not happen in local testing):

3 controller_impl::set_if_irreversible_block_num(uint32_t) ()
4 cotroller::process_vote_message( const vote_message& ) ()
5 controller_impl::create_and_send_vote_msg()
...
9 name_thread_pool<controller_impl::chain> run_thread()

The issue was when processing its own vote, create_and_send_vote_msg posts process_vote_message to the thread pool with a reference which can be destructed before its use.