Null locale causing the VTS fail.

Added a null check to avoid exceptions caused by timing delay during VTS run.This case fail is because AccessibilityWindowQueryActivity execute scheduleTraversals before Activity destroyed and execute doTraversal after Activity destroyed. This means window animation is not stop after AccessibilityWindowQueryActivity is destroyed and this will lead to test crash.

Test: Tested 5 times and it is passed 5 times.
Bug: 121169721
Change-Id: I915d46f925fb7a5ca43cac3ef3a343822b952b02