Ensure that SEXP shudown is before script shutdown (#4503)

* Ensure that SEXP shudown is before script shutdown

* Move before scpui destroy call

Author: BMagnu

freespace2/freespace.cpp

@@ -6683,11 +6683,14 @@ void game_shutdown(void)
 		gr_clear();
 		gr_flip();
 	}
-
+	
+	// Free SEXP resources
+	sexp_shutdown();
+	
 	// Free the scripting resources of the new UI first
 	scpui::shutdown_scripting();
 
-	// Everything after this should be done without scripting so we can free those resources here
+	// Everything after this should be done without scripting so we can free those resources here. By this point, all things that hold Lua References must be destroyed (such as Lua SEXPs)
 	Script_system.Clear();
 
 	// Deinitialize the new UI system, needs to be done after scripting shutdown to make sure the resources were
@@ -6729,8 +6732,6 @@ void game_shutdown(void)
 
 	scoring_close();
 
-	// Free SEXP resources
-	sexp_shutdown();
 
 	stars_close();			// clean out anything used by stars code