avcodec/libdav1d: Don't leak side-data-only packets

Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/libdav1d.c

@@ -328,6 +328,9 @@ static int libdav1d_receive_frame(AVCodecContext *c, AVFrame *frame)
                     return res;
                 }
             }
+        } else if (res >= 0) {
+            av_packet_unref(&pkt);
+            return AVERROR(EAGAIN);
         }
     }