Avert potential crashes in NotificationChildrenContainer.getMinHeight

It's unclear if these crashes are causing the setup wizard hang in the
bug or if these crashes and the hang share a common root cause, but
convert them to logged errors just in case.

Bug: 231915007
Test: atest PlatformScenarioTests
Change-Id: I89892bd2cae8e99040cd0636b1d1f775c4d97653