Add initialisation of p_dec->fmt_out so it can be used inside transcode to determine the decoders output format.

Revert change of: VLC_FOURCC('Y','U','V','P') into p_region->fmt.i_chrom on line 449 and fixed some identation for readibility.

- in Add() made osd transcoding selection part of else if
- copy region picture width/height to new region
- added some more debugging
- some cleanup

However not all bugs are gone. Need to figure out where they are.