ffplay: Fix -vismv

Fixes Ticket164
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffplay.c

@@ -1622,7 +1622,7 @@ static int input_request_frame(AVFilterLink *link)
     if (ret < 0)
         return -1;
 
-    if(priv->use_dr1) {
+    if(priv->use_dr1 && priv->frame->opaque) {
         picref = avfilter_ref_buffer(priv->frame->opaque, ~0);
     } else {
         picref = avfilter_get_video_buffer(link, AV_PERM_WRITE, link->w, link->h);

libavcodec/mpegvideo.c

@@ -1410,6 +1410,7 @@ void ff_print_debug_info(MpegEncContext *s, AVFrame *pict){
             pict->data[i]= s->visualization_buffer[i];
         }
         pict->type= FF_BUFFER_TYPE_COPY;
+        pict->opaque= NULL;
         ptr= pict->data[0];
         block_height = 16>>v_chroma_shift;