Should check isDeviceSecure in shouldConfirmCredentials

The NPE is because createConfirmDeviceCredentialIntent returns a null
intent when it founds that user does not set a secure lock.
So the fix is we should check is the user set a secure lock screen as well.

The reason the crash only happens in multi-window flow because
we have null checking in
the normal flow (i.e. interceptWithConfirmCredentialsIfNeeded).
But I think we better check it explicitly.

Bug: 28716456
Change-Id: Ib204cd02c0007bd1df36908bb3b5254ec4ffb914