Only use VDPAU hwaccel API for mpeg container

The use of VDPAU hwaccel API was an attempt to fix #11377. However, the underlying problem is a FFmpeg libavformat bug (https://trac.ffmpeg.org/ticket/2915).

FFmpeg 1.2's VDPAU hwaccel is clearly unstable. 24fps AVI would play at half that rate, cause crashes with nouveau or visual distortion with AMD

As the aim is only to fix #11377, only enable the hwaccel API for the mpeg container.

Add a "vdpauhwaccel" setting override to completely disable VDPAU hwaccel under all circumstances

Fixes #12162
Remove hack forcing MPEG1 video to be treated as MPEG2

This hack was added to fix #287, which was a problem with XvMC decoding.
It makes no sense today, and actually break genuine MPEG1 videos.

Fixes #12160

(cherry picked from commit fee00c36f79dd06432392dd9d4891efc5d253fd2)
Don't attempt to issue DB query if there's nothing to do

Prevent harmless SQL statement error messages to be logged when the position map is empty

Regression introduced in b4be8e24f9fab5b6a71f62df8e2c0403bedf4805

Fixes #12161

(cherry picked from commit d90af2d6b09bc5197a39d1e1d09baff2aafe9a2a)