DVB: Simplify the statistics interfaces handling.

Simplify ada3ea6714e7c5f11e73df27aa7123c5a491e362 and cec98b16291eee027e726a9ff4a481f13ef59221.
DirectShow graph manager: Use the real filter name for source filters.

Previously the filename was used instead.
Fix "On top while playing video" after 6cbe725c8b755854d37a6f46cb603e9f48116655.

The "on top" flag was lost when exiting the full screen mode.
Update checker: Properly close the CInternetFile object.

This commit fixes a warning about "destroying an open CInternetFile" in debug mode.