Convert "selected_tuple" into local function variable

game/src/chapter_select.rpy

@@ -20,13 +20,13 @@ define tuples_index = [
     ("Chapters 7 to 11", chapter_tuple_2)
 ]
 
-default selected_tuple = None
-
 
 init python:
 
     def select_chapter():
-        global selected_tuple, current_chapter, is_end_reached
+        global current_chapter, is_end_reached
+
+        selected_tuple = ()
 
         while True:
             selected_tuple = display_tuple_menu(tuples_index)