avformat/dvdvideodec: check the length of a NAV packet when reading titles

Some discs present titles with bogus NAV packets. We apply this check
for menus and for title MPEG blocks, but we should also apply it
for NAV packets during title demuxing.

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

libavformat/dvdvideodec.c

@@ -740,6 +740,13 @@ static int dvdvideo_play_next_ps_block(AVFormatContext *s, DVDVideoPlaybackState
                     return AVERROR_EOF;
                 }
 
+                if (nav_len != DVDVIDEO_BLOCK_SIZE) {
+                    av_log(s, AV_LOG_ERROR, "Invalid NAV packet size (expected=%d actual=%d)\n",
+                                            DVDVIDEO_BLOCK_SIZE, nav_len);
+
+                    return AVERROR_INVALIDDATA;
+                }
+
                 e_pci = dvdnav_get_current_nav_pci(state->dvdnav);
                 e_dsi = dvdnav_get_current_nav_dsi(state->dvdnav);