Fine-tune adlist:adte_modified trigger and don't default new date_updated column to now but use NULL instead

Signed-off-by: DL6ER <dl6er@dl6er.de>

advanced/Scripts/database_migration/gravity/12_to_13.sql

@@ -6,6 +6,13 @@ BEGIN TRANSACTION;
 
 ALTER TABLE adlist ADD COLUMN date_updated INTEGER;
 
+DROP TRIGGER tr_adlist_update;
+
+CREATE TRIGGER tr_adlist_update AFTER UPDATE OF address,enabled,comment ON adlist
+    BEGIN
+      UPDATE adlist SET date_modified = (cast(strftime('%s', 'now') as int)) WHERE id = NEW.id;
+    END;
+
 UPDATE info SET value = 13 WHERE property = 'version';
 
 COMMIT;