Text subtitles: Fix color parsing after 1f6b129d65e8de158e1119b348e59ac43d5ff7e6.

All values bigger than LONG_MAX were truncated to LONG_MAX.

Fixes #4619.
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...