Fix regression with MySQL

Fixes #4430 and #4431

app/Model/ProjectModel.php

@@ -89,11 +89,15 @@ class ProjectModel extends Base
     public function getByIdWithOwnerAndTaskCount($project_id)
     {
         return $this->db->table(self::TABLE)
-            ->columns(self::TABLE.'.*', UserModel::TABLE.'.username AS owner_username', UserModel::TABLE.'.name AS owner_name', 'SUM(CAST('.TaskModel::TABLE.'.is_active AS INTEGER)) AS nb_active_tasks')
+            ->columns(
+                self::TABLE.'.*',
+                UserModel::TABLE.'.username AS owner_username',
+                UserModel::TABLE.'.name AS owner_name',
+                "(SELECT count(*) FROM tasks WHERE tasks.project_id=projects.id AND tasks.is_active='1') AS nb_active_tasks"
+            )
             ->eq(self::TABLE.'.id', $project_id)
             ->join(UserModel::TABLE, 'id', 'owner_id')
             ->join(TaskModel::TABLE, 'project_id', 'id')
-            ->groupBy(self::TABLE.'.id', UserModel::TABLE.'.username', UserModel::TABLE.'.name')
             ->findOne();
     }