ffplay: fix -vismv 1

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -1699,7 +1699,7 @@ static int video_thread(void *arg)
 
         frame->pts = pts_int;
         frame->sample_aspect_ratio = av_guess_sample_aspect_ratio(is->ic, is->video_st, frame);
-        if (is->use_dr1) {
+        if (is->use_dr1 && frame->opaque) {
             FrameBuffer      *buf = frame->opaque;
             AVFilterBufferRef *fb = avfilter_get_video_buffer_ref_from_arrays(
                                         frame->data, frame->linesize,