add one missing check for stream existence in read_elst, fix #1364

Originally committed as revision 19792 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mov.c

@@ -1905,9 +1905,13 @@ free_and_return:
 /* edit list atom */
 static int mov_read_elst(MOVContext *c, ByteIOContext *pb, MOVAtom atom)
 {
-    MOVStreamContext *sc = c->fc->streams[c->fc->nb_streams-1]->priv_data;
+    MOVStreamContext *sc;
     int i, edit_count;
 
+    if (c->fc->nb_streams < 1)
+        return 0;
+    sc = c->fc->streams[c->fc->nb_streams-1]->priv_data;
+
     get_byte(pb); /* version */
     get_be24(pb); /* flags */
     edit_count = get_be32(pb); /* entries */