Fix artifacts of MPEG4-720I-DN-SV8K.trp caused by lack of IDR pictures and

subsequent zero POC value.

Originally committed as revision 15194 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -2215,6 +2215,7 @@ static av_cold int decode_init(AVCodecContext *avctx){
 
     h->thread_context[0] = h;
     h->outputed_poc = INT_MIN;
+    h->prev_poc_msb= 1<<16;
     return 0;
 }