Fix: WindowManagerGlobal#setStoppedState failed by IOOBE

Symptom:
An application crashed due to IndexOutOfBoundsException.
The exception was thrown at WindowManagerGlobal#setStoppedState.

Root cause:
setStoppedState invokes setWindowStopped for each ViewRoot by
ascending order. If an application removes its view within the
loop, loop index exceeds the number of items.

Solution:
Loop in descending order.

Bug: 69018607
Change-Id: I7e20282dc99b767912be4e00d81ffb49fe6c7ac0