[xbmc] [ffmpeg] avoid h264 decoder starting on wrong field

@elupus you fixed a problem once upon a time (green artefacts when switching between udp streams):
http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/136848

i think the codebase is quite different from the one i applied your fix:
https://github.com/at-visions/xbmc/commit/344b8b4049feb7d5ade0bafdd1595fd2419b0696

i just changed s/s0 to h/h0 but I'm not sure if this is right or if this fix is needed at all?