avcodec_default_get_buffer: init picture parameters.

Fixes multithreading regression introduced in 64c06615d2
Fixes ticket197
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/utils.c

@@ -351,6 +351,10 @@ int avcodec_default_get_buffer(AVCodecContext *s, AVFrame *pic){
         pic->pkt_pos = -1;
     }
     pic->reordered_opaque= s->reordered_opaque;
+    pic->sample_aspect_ratio = s->sample_aspect_ratio;
+    pic->width               = s->width;
+    pic->height              = s->height;
+    pic->format              = s->pix_fmt;
 
     if(s->debug&FF_DEBUG_BUFFERS)
         av_log(s, AV_LOG_DEBUG, "default_get_buffer called on pic %p, %d buffers used\n", pic, s->internal_buffer_count);