[Fix] Store subtitle settings only on user action

This is a follow-up on PR https://github.com/xbmc/xbmc/pull/4921.
Video settings are now stored **only** on user actions.

Thanks @Voyager1 for your help!
you're right... It seems that for DVDs, once the setting is saved, it always needs to be saved so that we have consistency between the saved setting and the state of the navigator which is also saved. Otherwise, if we have not saved it, auto-selection and the state of the dvd navigator should bring back the same selection upon resume.
Alternatively, we could NOT use the subtitle setting upon resume of a DVD, let the navigator decide. That would also resolve the inconsistency...