lavfi/metadata: fix metadata deletion if comparison returns false

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>

libavfilter/f_metadata.c

@@ -330,9 +330,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
     case METADATA_DELETE:
         if (!s->key) {
             av_dict_free(metadata);
-        } else if (e && e->value && s->value && s->compare(s, e->value, s->value)) {
-            av_dict_set(metadata, s->key, NULL, 0);
-        } else if (e && e->value) {
+        } else if (e && e->value && (!s->value || s->compare(s, e->value, s->value))) {
             av_dict_set(metadata, s->key, NULL, 0);
         }
         return ff_filter_frame(outlink, frame);