EVR-CP and Sync renderers: Remove useless use of interlocked functions.

The critical sections are lock protected so there is no need for interlocked functions which is a good thing being that those functions were badly used and did not protect anything anyway.

Fixes CID 1249711 and CID 1249712.
MediaInfo tab: Enable the "Save As" button only if some info is available.

Being that the tab can be displayed before the info is available or even if none could be found, it makes sense to disable the button in those cases.
DSUtil: Remove duplicated function "FileExists".
Cosmetics: Remove unused include.
DSUtil: Remove duplicated function GetProgramPath.
Cosmetics: Use PathUtils::GetProgramPath when possible.
VSFilter: Remove an unused function.
Cosmetics: External toolbar image: Replace nested if by loops.
AStyle: Increase max-instatement-indent from 40 to 50.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
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...