users: do nothing when nothing to update

src/users.js

@@ -642,6 +642,7 @@ async function update(user, data, auditSource) {
             args.push(data[k]);
         }
     }
+    if (args.length == 0) return; // nothing to do
     args.push(user.id);
 
     const [error, result] = await safe(database.query('UPDATE users SET ' + fields.join(', ') + ' WHERE id = ?', args));