fix audio/sub id selection in gui dialog at initial play

fixes incomplete and partially correct behavior from https://github.com/FernetMenta/xbmc/commit/30e103633a1d4d0ee573e1ece6af3fed4cd3ebfe

The issue was that the stream ID was not known yet so that GetAudioStream() or GetSubtitle() can't find the right stream. This is fixed by setting the currentstream id prior to the call to GetAudioStream/Subtitle. 
At least, this way, the GUI is now back in line with the selected stream.

This was an issue with especially DVDs that set the stream through dvd menus, or when the mKV container had default stream(s).