Propagate errors from PostConnect to the filter graph.

This fixes an issue when DXVA2 Native is refused during PostConnect,
and the software decoder is unavailable (wmv9 dmo not present)
Destruct the decoder object when init failed.

This avoids a half-initialized decoder lingering around and possibly
causing issues.
Check that the decoder object exists before dispatching commands to it.

This fixes an occasional crash when the decode thread enters an
unpredicted error state.
Fallback to avcodec for WMV3/VC-1 if the DMO decoder is not available.
[MPC-HC] Use our own ffmpeg clone repository.

WARNING: This should be the first custom commit in our fork and its title should not be modified.
[MPC-HC] LAV Splitter: Exhibits MKV attachments through IDSMResourceBag interface.
[MPC-HC] Tray icon: Add an optional custom callback for "show property page" events.
[MPC-HC] Fix the include directories for FFmpeg's out-of-source-tree build.
[MPC-HC] Version number: Add a "git describe based" commit number to identify the vanilla LAV Filters we are based on.

This way if we distribute LAV Filters version X.Y.Z.N, it means that our custom build is based on:
 - the stable version X.Y.Z,
 - with N official patches (which will be part of next official LAV Filters build),
 - and some custom non-official patches which are here to improve the integration in MPC-HC.