clapper: Skip default cache location set at item construction

It is already NULL for newly created media item and otherwise
debug printing for this property being changed to NULL for each
media item is confusing

src/lib/clapper/clapper-media-item.c

@@ -770,6 +770,9 @@ clapper_media_item_update_from_parsed_playlist (ClapperMediaItem *self, GListSto
 void
 clapper_media_item_set_cache_location (ClapperMediaItem *self, const gchar *location)
 {
+  if (!self->cache_uri && !location)
+    return; // No change (called during construction)
+
   g_clear_pointer (&self->cache_uri, g_free);
 
   if (location)