Make sure the EC code does not attempt to use inter based concealment if there

is no reference frame available. (this can happen because the EC code will attempt
to use reference frames even for I/IDR frames)

Originally committed as revision 22732 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/error_resilience.c

@@ -629,6 +629,12 @@ static int is_intra_more_likely(MpegEncContext *s){
             undamaged_count++;
     }
 
+    if(s->codec_id == CODEC_ID_H264){
+        H264Context *h= (void*)s;
+        if(h->ref_count[0] <= 0 || !h->ref_list[0][0].data[0])
+            return 1;
+    }
+
     if(undamaged_count < 5) return 0; //almost all MBs damaged -> use temporal prediction
 
     //prevent dsp.sad() check, that requires access to the image