Corrects wrong activity sent for resume in canMoveTaskToBack

When evaluating moveTaskToBack, the resuming activity should be
searched from the next task, rather than the current task. Also there
can skip querying from controller if the task is already bottommost.

Flag: EXEMPT bugfix
Bug: 401518213
Test: monkey
Change-Id: Id9c73ab55b08af107f467b4274f87818ab182625