nutdec: Flip the direction for seeking with an index in the failure case.

This is closer to how seeking works without an index
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/nutdec.c

@@ -950,6 +950,8 @@ static int read_seek(AVFormatContext *s, int stream_index,
 
     if (st->index_entries) {
         int index = av_index_search_timestamp(st, pts, flags);
+        if (index < 0)
+            index = av_index_search_timestamp(st, pts, flags ^ AVSEEK_FLAG_BACKWARD);
         if (index < 0)
             return -1;