Fixed a bug with negative-rate scaled content time conversion

ODIDDataSource.preroll_mp4_resource() had an issue with processing the
 TimeSeekRange response values for negative-rate play speeds.

Also added some debug.

Tested with TimeSeekRange with npt=15-10 and PlaySpeed with speed=-2 on
 B-AVC_MP4_MP_SD-01.-2_1.MP4. But the duration of the file comes out smaller
 than the converted values - causing the effective time to be incorrect.
 Will open a bug for the issue.