Fixing crash when dismissing last stack task.

- The crash was due to us trying to get an anchor task when there were
  no more tasks in the stack.  The original call to check the stack
  task count was poorly named so updating the name of that call as well.

Bug: 26500050

Change-Id: I9652e90a6a2e19008c5c84ce877afca576b3175f
9 files changed