Avoid locking profile task when it is already lock

WorkLockActivity was started repeatedly on top of the
task that contains work apps when turning screen on
and off over and over. So, lots of the WorkLockActivity
instances were created and added in the task, which
caused system sluggish.

Bug: 168527567
Bug: 177457096
Bug: 191385314
Test: manually test work challenges
Test: RootWindowContainerTests
Change-Id: Iac345471ef3badad6b9e5c0cc2873c60938663eb