Check isInteractive after traversal before hiding keyguard.

The Runnable passed to postAfterTraversal is capable of
unilaterally hiding the keyguard, but it's run at an
indeterminate time due to the postAfterTraversal. To be
safe, check the earliest source of truth (PowerManager)
to see if we're still interactive before proceeding.

Fixes: 296886973
Test: lock the device during the unlock animation from bouncer to an app
Test: atest SystemUITests
Change-Id: Iaef7cff8366015c3e66aac4d740f6240e7c183db