seek back at the end of file after updating header

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@7473 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/swf.c

@@ -691,6 +691,7 @@ static int swf_write_trailer(AVFormatContext *s)
         put_le32(pb, file_size);
         url_fseek(pb, swf->duration_pos, SEEK_SET);
         put_le16(pb, video_enc->frame_number);
+        url_fseek(pb, file_size, SEEK_SET);
     }
 
     av_free(swf->audio_fifo);