avplay: Check memory allocation

Bug-Id: CID 1288294
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

avplay.c

@@ -1580,6 +1580,8 @@ static int video_thread(void *arg)
     AVFilterContext *filt_out = NULL, *filt_in = NULL;
     int last_w = is->video_st->codec->width;
     int last_h = is->video_st->codec->height;
+    if (!graph)
+        return AVERROR(ENOMEM);
 
     if ((ret = configure_video_filters(graph, is, vfilters)) < 0)
         goto the_end;