fftools/ffmpeg: Free swresample dictionary during cleanup

Freeing this was forgotten in ad899522.

Fixes #8315 and #8316.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 6f2a3958cf)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

fftools/ffmpeg.c

@@ -553,6 +553,7 @@ static void ffmpeg_cleanup(int ret)
         ost->audio_channels_mapped = 0;
 
         av_dict_free(&ost->sws_dict);
+        av_dict_free(&ost->swr_opts);
 
         avcodec_free_context(&ost->enc_ctx);
         avcodec_parameters_free(&ost->ref_par);