fftools/ffplay: fix possible memory leak in decoder

Fixes ticket #8549.
Signed-off-by: Marton Balint <cus@passwd.hu>

fftools/ffplay.c

@@ -644,7 +644,10 @@ static int decoder_decode_frame(Decoder *d, AVFrame *frame, AVSubtitle *sub) {
                 if (packet_queue_get(d->queue, &pkt, 1, &d->pkt_serial) < 0)
                     return -1;
             }
-        } while (d->queue->serial != d->pkt_serial);
+            if (d->queue->serial == d->pkt_serial)
+                break;
+            av_packet_unref(&pkt);
+        } while (1);
 
         if (pkt.data == flush_pkt.data) {
             avcodec_flush_buffers(d->avctx);