Subtitles: Improve error checking with ASS rendering.

Some crashes could occur when the SSA script was using obviously wrong values.

Uses the same check as libass for maximum glyph size.

Backport of MPC-HC commit 2c597d9
Subtitles: Make both DVD subtitles show in case of overlap

Makes behavior consistent with VLC and mplayer/libavcodec DVD
subtitle implementations. Sets the StopTime of the subtitle
before the same as the StartTime of the currently added DVD
subtitle.

Backport of MPC-HC commit f478e57
Merge with MPC-HC commit 9f504fcfb79dd05a14b0ef45682b6719fa4a849a

* VobSubFile: Use TRACE for debug messages.

We don't want to spam the users with probably useless error messages.

Thanks to clsid.
(CCCP Patch) Add Lord's extra colorspace conversion code paths to vd.cpp/h

Also actually use them in BaseVideoFilter, and add a minor separate modification
regarding NV12 positioning in DoCheckTransform().