Fix NPE from LockScreenSession#unlockDevice

CipherTest also use LockScreenSession to clear the test settings.
But since it's not WindowManager test, so the mWmState is never
been compute, which cause it from crash while access it.

Bug: 150195358
Test: atest CipherTest#testCanCreateAuthBoundKeyWhenScreenLocked
Change-Id: Ifecc4fc2823a999809a4f2a2af3582e248044d85
1 file changed