MDEV-26890 : Crash on shutdown, with active binlog dump threads

The reason for the crash was a bug in MDEV-19275, after which shutdown
does not wait for binlog threads anymore.

sql/mysqld.cc

@@ -1787,7 +1787,7 @@ static void close_connections(void)
 
   /* Kill phase 2 */
   server_threads.iterate(kill_thread_phase_2);
-  for (uint64 i= 0; THD_count::connection_thd_count(); i++)
+  for (uint64 i= 0; THD_count::value() > local_connection_thread_count; i++)
   {
     /*
       This time the warnings are emitted within the loop to provide a