Updated LAV Filters to 0.62-12-f949463 (custom build based on 0.62-5-a731178)

Important changes:
 - LAV Video: Fix a crash with DVD subtitles on 64-bit builds when using software decoding (fixes #4539).
 - LAV Splitter: Fix palette for VobSub tracks in MP4 (fixes #4639).
Comment out some unused variable assignments.

Those can be useful if the functions are extended one day.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
Why "C:\tmp.srt"?
WebUI: Inform the web interface that no audio stream is available.
WebUI: Make use of new [hasaudio] info.
What the hell was intended here?!

Trying to make some sense of that code. Without much luck so far...