Prevent IndexOutOfBoundsException while removing activities

IndexOutOfBoundsException was thrown when traversing the Task
from bottom to top because the activity could be removed from
the Task and the activities are less than its original size.

Bug: 249658397
Bug: 260643770
Test: 1) Start multiple activities in a Task
      2) Swipe up to home
      3) Kill the app process from shell
      4) Remove the task from Recents
Change-Id: I64955415c04da30d7dc8a4681474ceb06db1e88b
Merged-In: I64955415c04da30d7dc8a4681474ceb06db1e88b