give chance to terminate in wait_for_sys too (was just check_for_sys)

lib/sel.ml

@@ -157,7 +157,10 @@ let rec wait_for_system_or_queue_events ~deadline (fds,sys) queue =
     let ready_sys, waiting_sys, min_prio_sys = pull_ready ~advance:advance_system ready_fds sys in
     let ready_queue, waiting_queue, min_prio_queue = pull_ready ~advance:advance_queue () queue in
     if ready_sys <> Sorted.nil || ready_queue <> Sorted.nil
-    then ready_sys, ready_queue, waiting_sys, waiting_queue, Sorted.min_priority min_prio_queue min_prio_sys
+    then
+      let min_prio =  Sorted.min_priority min_prio_queue min_prio_sys in
+      let new_ready_sys, waiting_sys, min_prio_new_ready_sys = check_for_system_events min_prio waiting_sys in
+      Sorted.append new_ready_sys ready_sys, ready_queue, waiting_sys, waiting_queue, Sorted.min_priority min_prio_new_ready_sys min_prio
     else wait_for_system_or_queue_events ~deadline (fds,waiting_sys) queue
 
 let wait_for_system_or_queue_events ~deadline sys queue =