Update LAV Filters to version 0.58.2-45-gf93cb2e

Important changes:
 - This update fixes an issue with LAV Audio Decoder mixer feature (fixes #3348).
 - This update fixes an issue with LAV Video Decoder where some Xvid files showed corruption (fixes #3368).
 - LAV Splitter can now connect to the VTS Reader source filter (used to open IFO files).
build_lavfilters.bat: Ensure compilation failures are properly detected.
ShockwaveGraph: restore process volume on exit

Applies to Vista and later.
Fixes #2852
Rewritten code for auto-load subtitles and support for '_' as a separator.

Being a video file named video.ext, video_whatever.srt will now be auto-loaded.

This commit fixes #3195.
Give "Prefer external subtitles over embedded subtitles" option precedence over language matches.