Fix transition between two occluding activities

This fixes an issue when starting an activity that occldues
Keyguard with the window flag from an activity that is already
occluding Keyguard. Normally we wait until the transition starts
until the next activity had a chance to set its layout flag
(FLAG_SHOW_WHEN_LOCKED) with the UnknownVisibilityController.

Now, since setAppVisibility(false) was called after immediately
starting the activity, we removed the activity immediately from
the UnknownVisibilityController waiting list and then unoccluded
Keyguard.

We fix this by only removing the activity from the waiting list if
the app is actually hidden and not just because it's hidden by
Keyguard.

This regressed from I745e985766a1af97203e1d22b6443dabdd0c0363
because calling setVisible(true) was setting the token's visible
to true. Then, setVisible(false) was NOT ignored anymore.
Previously it was just ignored because the app wasn't made visible
yet from WM perspective.

Test: go/wm-smoke
Test: android.server.cts.KeyguardTransitionTests#testNewActivityDuringOccluded
Test: Launch camera from Keyguard with animation transition scale
set to 0. (regression test)

Change-Id: I36ec1bf335c48baf298e78620381bdd0be34aa1d
Fixes: 65061212
Bug: 37677242