When expand[]=subtasks is used, the LEFT JOIN on task_relations filters
out same-project subtasks. If a parent task was deleted, the JOIN
produces NULL for parent_tasks.id/project_id, and since NULL != value
evaluates to NULL (not TRUE) in SQL, these tasks were incorrectly
excluded.
Add builder.IsNull{"parent_tasks.id"} to the OR condition so tasks
whose parent was deleted are still included in results.
e7b693c788