Fix crash when OverviewCommandHelper queue is cleared before callback response

This issue should not happen after b/364860731 fix. The issue happened because the queue was cleared while a command was being processed. Then, onTransitionComplete callback returned and checked if the first item of the queue was the same processed, but the queue was empty.
To prevent future cases of NoSuchElementException, we updated the logic to check the firstOrNull item from the queue.

Fix: 364986456
Bug: 364860731
Flag: EXEMPT bugfix
Test: Manual
Change-Id: Iaa606943db3ff89a7f3012260663c41954d720a7