DVDNav: fix dvdnav_describe_title_chapters crash

Close #6578

contrib/src/dvdnav/libdvdnav-searching.c-check-cellnr-before-indexing.patch

+diff --git a/src/searching.c b/src/searching.c
+index 3649e9d..0b5f22a 100644
+--- a/src/searching.c
++++ b/src/searching.c
+@@ -640,7 +640,11 @@ uint32_t dvdnav_describe_title_chapters(dvdnav_t *this, int32_t title, uint64_t
+       goto fail;
+     }
+ 
+-    cellnr = pgc->program_map[ptt[i].pgn-1];
++    if ((cellnr = pgc->program_map[ptt[i].pgn-1]) == 0) {
++      printerr("Cell new row cannot be 0");
++      continue;
++    }
++
+     if(ptt[i].pgn < pgc->nr_of_programs)
+       endcellnr = pgc->program_map[ptt[i].pgn];
+     else

contrib/src/dvdnav/rules.mak

@@ -18,6 +18,7 @@ $(TARBALLS)/libdvdnav-$(LIBDVDNAV_VERSION).tar.bz2:
 dvdnav: libdvdnav-$(LIBDVDNAV_VERSION).tar.bz2 .sum-dvdnav
 	$(UNPACK)
 	$(APPLY) $(SRC)/dvdnav/dvdnav.patch
+	$(APPLY) $(SRC)/dvdnav/libdvdnav-searching.c-check-cellnr-before-indexing.patch
 	$(MOVE)
 
 DEPS_dvdnav = dvdcss dvdread