[DATABASE] Always quote identifiers

The code used to operate under the assumption that MariaDB doesn't support
quoting identifiers. Not only is that not exactly true, but MariaDB has
reserved keywords that cannot be used as table or column names unquoted.

plugins/Nodeinfo/actions/nodeinfo_2_0.php

@@ -326,15 +326,18 @@ class Nodeinfo_2_0Action extends Action
      */
     public function getActiveUsers(int $days): int
     {
+        $userTable = common_database_tablename('user');
         $query = "
-         SELECT COUNT(DISTINCT profile_id) as active_users_count
+         SELECT COUNT(DISTINCT profile_id) AS active_users_count
          FROM (
-            SELECT profile_id FROM notice WHERE notice.created >= NOW() - INTERVAL {$days} DAY AND notice.is_local = 1
+            SELECT profile_id FROM notice
+               WHERE notice.created >= (CURRENT_TIMESTAMP - INTERVAL {$days} DAY) AND notice.is_local = 1
             UNION ALL
-            SELECT user_id FROM fave INNER JOIN user ON fave.user_id = user.id WHERE fave.created >= NOW() - INTERVAL {$days} DAY
+            SELECT user_id FROM fave INNER JOIN {$userTable} ON fave.user_id = {$userTable}.id
+               WHERE fave.created >= (CURRENT_TIMESTAMP - INTERVAL {$days} DAY)
             UNION ALL
-            SELECT id FROM user WHERE user.created >= NOW() - INTERVAL {$days} DAY
-         ) as source";
+            SELECT id FROM {$userTable} WHERE {$userTable}.created >= (CURRENT_TIMESTAMP - INTERVAL {$days} DAY)
+         ) AS source";
 
         $activeUsersCount = new DB_DataObject();
         $activeUsersCount->query($query);