PGS Subtitles: Fix random issues (wrong timing, missing subs, etc.).

PGS subtitles rendering had become erratic after 67623aac17467165d2423a551de6f06022e1d01c.

Refs: #3691.
Changelog: Add the ticket number corresponding to "Language" menu removal.

I had forgotten we had a ticket for that.

Fixes #4144.
VSFilter: Use the same subtitle names as the ISR for external subtitles.

Use the video filename to be able to extract more information from the subtitle filenames.
Why "C:\tmp.srt"?
Fix some CPPCheck warnings or mark them as intentional.
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...
Fix: x86 and x64 versions conflicted over file associations.

4f465cf8b81f1da800b1bfc57cc48e317d24fbb5 was incomplete for Vista+.

This commit fixes #4064.