[videplayer][pvr] Fix a crash when stopping playback while teletext is opened.

[ace20022]

Call chain:

CGUIDialogTeletext::OnInitWindow -> CTeletextDecoder::InitDecoder() -> 
CApplicationPlayer::GetTeletextCache() -> VideoPlayerTeletex::GetTeletextCache()

Now GUIDialogTeletext access the cache via the pointer hold by the TeletextDecoder. It points to a member variable of VideoPlayerTeletex. When playback is stopped the VideoPlayer deletes its VideoPlayerTeletex.
Later the dialog calls its OnDeinitWindow method and that calls CTeletextDecoder::EndDecoder() which tries to access the cache.

[FernetMenta]

looks good

[ghost]

Now the active page gets lost when leaving and re-entering teletext, and I'm reset to the default #100. I'd be glad if that could be fixed.
Btw.: I'd appreciate [a configuration option] to get rid of the fading effect when entering/leaving teletext.
Milhouse suggested an Estuary feature request, but all other skins I've checked show the same behaviour, so it's probably located elsewhere (Player?).

[ace20022]

I'd be glad if that could be fixed.

I think I know why this happens. I'll try to fix it.