Ensured debug mode key handlers always exist

Before this commit the debug console's key handler wasn't added to saved games which didn't have it because they weren't started with debugging enabled and the debug script's key handler would
only be added to saved games older than 85 when debugging was enabled. So if debugging was enabled for a saved game newer than 85 the key handler for the debug script would be missing.
@TheCycoONE I could modify addKeyHandler() in this pull request to make sure it can't add duplicate key handler responses.