Add NPE chceck in CameraTransitionCallback

Initialized mCutoutView introduce performance regression in
SystemUIBootTiming_StartServicescom

Check Null in traverse mCutoutViews loop since not all mCutoutViews[pos]
be inflated at the meanwhile

Test: boottime_test
Test: manual boot without crash
Bug: 151986151
Change-Id: Iba8e07a1304f3e07c89de6d4e223b620bd88b7d3