Only need to wait for a single scheduler thread to become active (#4544)

Prior to this commit, ponyint_sched_maybe_wakeup_if_all_asleep would
wait until the number of active scheduler check variable matched
the active schedule count variable. This could potentially cause it
to unnecessarily wait for more than 1 scheduler thread to become
fully active.

This commit changes the logic to only wait until the active
scheduler check variable indicates that there is at least one
fully active scheduler.

src/libponyrt/sched/scheduler.c

@@ -1474,7 +1474,7 @@ void ponyint_sched_maybe_wakeup_if_all_asleep(int32_t current_scheduler_id)
     {
       // wait for sleeping threads to wake and update check variable
       // to ensure that we have at least one fully awake scheduler thread
-      while (get_active_scheduler_count() != get_active_scheduler_count_check())
+      while (get_active_scheduler_count_check() == 0 && get_active_scheduler_count() > 0)
       {
         // send signals to all scheduler threads that should be awake
         // this is somewhat wasteful if a scheduler thread is already awake