ffplay: fix return value of get_video_frame if avcodec_decode_video fails

Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -1505,7 +1505,7 @@ static int get_video_frame(VideoState *is, AVFrame *frame, int64_t *pts, AVPacke
     }
 
     if(avcodec_decode_video2(is->video_st->codec, frame, &got_picture, pkt) < 0)
-        return -1;
+        return 0;
 
     if (got_picture) {
         int ret = 1;