[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!
update: indeed changing the FrameMove() code to 
```m_settingsManager->SetBool(SETTING_SUBTITLE_ENABLE, g_application.m_pPlayer->GetSubtitleVisible());``` solves the issue as well, but as I suspected, a change of setting through the dvd menu does not get saved, and as a result of that, stopping and resuming a movie is inconsistent in subtitle visibility.