Bug#23074173 - NUMBER OF WORKER THREADS GOES UNDER MYSQLX_MIN_WORKER_THREADS

Follow up push.
Orginal patch made another problem in scheduler.cc more frequent.
Added extra code in sychronized code which checks the state of
task queue before making the thread wait for signal.

Author: lkotula

mysql-test/suite/xplugin/r/bug23074173.result renamed to mysql-test/suite/xplugin/r/system_variable_min_worker_threads.result

@@ -230,6 +230,9 @@ bool Scheduler_dynamic::wait_if_idle_then_delete_worker()
   if (!is_running())
     return false;
 
+  if (!m_tasks.empty())
+    return false;
+
   int result = m_worker_pending_cond.timed_wait(m_worker_pending_mutex,
                                      m_idle_worker_timeout * MILLI_TO_NANO);