RegisterHotkeys: Fix a rare crash.

Use the Windows API more correctly and add more error checking.

This commit fixes #2971.
update ffmpeg (n0.8-19710-g35135a3)
Remove custom code needed in the past in order to successfully link ffmpeg library.
update h264_recov.c for the recent changes
Update our files for the recent FFmpeg changes.
H264 DXVA Decoder: Rewrote h264_dxva.c based on recent h264.c.
h264_dxva.c: update for the recent changes in ffmpeg
update ffmpeg (n0.8-20039-g7d15cd4)
MPCVideoDec: Fix compilation.
update CFLAGS and ffmpeg/config.asm and ffmpeg/config.h