SubPicAP: Fix unitialized field.

Fixes CID 966363
External PGS subtitles: Fail nicely when a file can't be opened.

This commit fixes #4363.
Fix drag-and-drop from some applications.

Drag-and-dropping a downloaded file from Chrome failed for example.

This commit fixes #3036.
ISR: Render text subtitles relative to the video frame when in doubt.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
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.
Auto mode for relative to.