Subtitle delay step tooltip: Show "<not defined>" when a hotkey isn't set.
"Subtitles" option page: Make the "Delay step" tooltip multiline.

Also fixes a truncation issue on some OS like Vista.

Fixes #4876.
Updated LAV Filters to 0.62-50-3c646ee (custom build based on 0.62-45-33f0b34).

Important changes:
 - LAV Audio and LAV Splitter: Fix TrueHD streams with a Dolby Atmos sub-stream (fixes #4879).
 - LAV Video: Experimental support for hardware (CUVID and DXVA2)  assisted decoding of HEVC streams (disabled by default) (fixes #4783).
 - Updated ffmpeg library.
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...