avformat/utils: add gif to tb_unreliable()

This improves the used timebases when gif is the source

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -2868,6 +2868,7 @@ static int tb_unreliable(AVCodecContext *c)
         // c->codec_tag == AV_RL32("XVID") ||
         c->codec_tag == AV_RL32("mp4v") ||
         c->codec_id == AV_CODEC_ID_MPEG2VIDEO ||
+        c->codec_id == AV_CODEC_ID_GIF ||
         c->codec_id == AV_CODEC_ID_H264)
         return 1;
     return 0;