Fix a bug where a pointer was cached to an array that might later move due to

patches/to_upstream/43_mkv_seekahead_revalidate.patch

Index: patches/to_upstream/43_mkv_seekahead_revalidate.patch
===================================================================
--- patches/to_upstream/43_mkv_seekahead_revalidate.patch	(revision 0)
+++ patches/to_upstream/43_mkv_seekahead_revalidate.patch	(revision 0)
@@ -0,0 +1,19 @@
+diff -wurp -N orig/libavformat/matroskadec.c patched-ffmpeg/libavformat/matroskadec.c
+--- orig/libavformat/matroskadec.c	2011-10-20 11:28:27.935337424 -0700
++++ patched-ffmpeg/libavformat/matroskadec.c	2011-10-20 11:32:03.845401593 -0700
+@@ -1241,7 +1241,6 @@ static int matroska_parse_seekhead_entry
+ static void matroska_execute_seekhead(MatroskaDemuxContext *matroska)
+ {
+     EbmlList *seekhead_list = &matroska->seekhead;
+-    MatroskaSeekhead *seekhead = seekhead_list->elem;
+     int64_t before_pos = avio_tell(matroska->ctx->pb);
+     int i;
+ 
+@@ -1251,6 +1250,7 @@ static void matroska_execute_seekhead(Ma
+         return;
+ 
+     for (i = 0; i < seekhead_list->nb_elem; i++) {
++        MatroskaSeekhead *seekhead = seekhead_list->elem;
+         if (seekhead[i].pos <= before_pos)
+             continue;
+