WIN_CLOSED bulk update. No more test for event is None, use WIN_CLOSED instead

DemoPrograms/Demo_Multithreaded_Long_Tasks.py

@@ -58,7 +58,7 @@ def the_gui():
     # --------------------- EVENT LOOP ---------------------
     while True:
         event, values = window.read(timeout=100)
-        if event in (None, 'Exit'):
+        if event in (sg.WIN_CLOSED, 'Exit'):
             break
         elif event.startswith('Do'):
             try: