fftools/ffmpeg_mux_init: don't free the AVDictionaryEntry until after it's been used

Signed-off-by: James Almer <jamrial@gmail.com>

fftools/ffmpeg_mux_init.c

@@ -2145,7 +2145,6 @@ static int of_parse_iamf_submixes(Muxer *mux, AVStreamGroup *stg, char *ptr)
 
                 if (e = av_dict_get(dict, "stg", NULL, 0))
                     idx = strtoll(e->value, &endptr, 0);
-                av_dict_set(&dict, "stg", NULL, 0);
                 if (!endptr || *endptr || idx < 0 || idx >= oc->nb_stream_groups - 1 ||
                     oc->stream_groups[idx]->type != AV_STREAM_GROUP_PARAMS_IAMF_AUDIO_ELEMENT) {
                     av_log(mux, AV_LOG_ERROR, "Invalid or missing stream group index in "
@@ -2166,6 +2165,7 @@ static int of_parse_iamf_submixes(Muxer *mux, AVStreamGroup *stg, char *ptr)
                     av_iamf_param_definition_alloc(AV_IAMF_PARAMETER_DEFINITION_MIX_GAIN, 0, NULL);
                 if (!submix_element->element_mix_config)
                     ret = AVERROR(ENOMEM);
+                av_dict_set(&dict, "stg", NULL, 0);
                 av_opt_set_dict2(submix_element, &dict, AV_OPT_SEARCH_CHILDREN);
             } else if (layout) {
                 AVIAMFSubmixLayout *submix_layout = av_iamf_submix_add_layout(submix);