Audio CDROM: Ensure the track number is valid before using it.

Fixes CID 1090495.
Simple text subtitles: Mark some helper functions static.
CTextFile: Faster ReadLine by reusing the string buffer when possible.

Around 5% faster.
CTextFile: Buffer the position when possible for faster UTF8 ReadString.

Around 10-15% faster.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
ISR: Render text subtitles relative to the video frame when in doubt.
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...
Fix: x86 and x64 versions conflicted over file associations.

4f465cf8b81f1da800b1bfc57cc48e317d24fbb5 was incomplete for Vista+.

This commit fixes #4064.
Auto mode for relative to.