Introduce non-null `itemInfo` inside TaskView

Let `TaskView` have a non-null `itemInfo` even it has no
tasks (no corresponding TaskContainer). Thus, we can still
go forward to log the necessary info of the `TaskView`
without any tasks.

Flag: EXEMPT refactor
Fix: 391918297
Test: TaskViewItemInfoTest
Change-Id: Idd08eb9846b1cd2043dd0087bc3e0078bb0b8247