h264_nal: fix h264_get_spspps
h264_nal: fix h264_get_spspps

Don't end the NAL unit when we reach 0x000000. Refactor since we don't need to
parse separately the start and the end of the NAL unit anymore.

vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,vlc-mirror/vlc