Dont try generic seek if seek request before first index entry and backward.

Fixes issue1275


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@21633 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/utils.c

@@ -1548,6 +1548,9 @@ static int av_seek_frame_generic(AVFormatContext *s,
 
     index = av_index_search_timestamp(st, timestamp, flags);
 
+    if(index < 0 && st->nb_index_entries && timestamp < st->index_entries[0].timestamp)
+        return -1;
+
     if(index < 0 || index==st->nb_index_entries-1){
         int i;
         AVPacket pkt;