avformat/dvdvideodec: move memcpy below missed NAV packet warning

Readability improvement; the warning can be bundled beneath
the preceding validations rather than awkwardly between the memcpy
and return.

Signed-off-by: Marth64 <marth64@proxyid.net>

libavformat/dvdvideodec.c

@@ -804,13 +804,13 @@ static int dvdvideo_play_next_ps_block(AVFormatContext *s, DVDVideoPlaybackState
                     return AVERROR_INPUT_CHANGED;
                 }
 
-                memcpy(buf, &nav_buf, nav_len);
-
                 if (state->pgn != cur_pgn)
                     av_log(s, AV_LOG_WARNING, "Unexpected PG change (expected=%d actual=%d); "
                                               "this could be due to a missed NAV packet\n",
                                               state->pgn, cur_pgn);
 
+                memcpy(buf, &nav_buf, nav_len);
+
                 (*p_nav_event) = nav_event;
 
                 state->is_seeking = 0;