Do not lose user flags when passing calls from the new to the old seeking API.

Originally committed as revision 17959 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -1601,7 +1601,7 @@ int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts, int
     //Fallback to old API if new is not implemented but old is
     //Note the old has somewat different sematics
     if(s->iformat->read_seek || 1)
-        return av_seek_frame(s, stream_index, ts, ts - min_ts > (uint64_t)(max_ts - ts) ? AVSEEK_FLAG_BACKWARD : 0);
+        return av_seek_frame(s, stream_index, ts, flags | (ts - min_ts > (uint64_t)(max_ts - ts) ? AVSEEK_FLAG_BACKWARD : 0));
 
     // try some generic seek like av_seek_frame_generic() but with new ts semantics
 }