h264dec: fail to decode a avc stream.

[feiwan1]

root@wangfei_skl:~/Downloads# yamidecode -i SliceHD.mpg -m 1
libva info: VA-API version 1.1.0
libva info: va_getDriverName() returns 0
libva info: User requested driver 'i965'
libva info: Trying to open /opt/yami/vaapi/lib/dri/i965_drv_video.so
libva info: Found init function __vaDriverInit_1_1
libva info: va_openDriver() returns 0
[h264 @ 0x2a10a40] SPS unavailable in decode_picture_timing
[h264 @ 0x2a10a40] non-existing PPS 1 referenced
[AVBSFContext @ 0x2a9c5a0] Invalid NAL unit 0, skipping.
[h264 @ 0x2a10a40] SPS unavailable in decode_picture_timing
[h264 @ 0x2a10a40] non-existing PPS 1 referenced
[h264 @ 0x2a10a40] decode_slice_header error
[h264 @ 0x2a10a40] no frame!
[h264 @ 0x2a10a40] SPS unavailable in decode_picture_timing
[h264 @ 0x2a10a40] non-existing PPS 1 referenced

This issue is come from gst-vaapi, and the stream can be found:
https://bugzilla.gnome.org/show_bug.cgi?id=796169