very small performance improvment

pkg/models/list_tasks_create_update.go

@@ -166,12 +166,14 @@ func (t *ListTask) updateTaskAssignees(assignees []*User) (err error) {
 	}
 
 	// Delete all assignees not passed
+	if len(assigneesToDelete) > 0 {
 		_, err = x.In("user_id", assigneesToDelete).
 			And("task_id = ?", t.ID).
 			Delete(ListTaskAssginee{})
 		if err != nil {
 			return err
 		}
+	}
 
 	// Get the list to perform later checks
 	list := List{ID: t.ListID}