Treat non-existing types as controllable types for compatibility

If a device doesn't have a navigation bar, the legacy system UI flag
framework would still work as if there is a navigation bar. This CL
makes the behavior compatible.

It has been broken since cfebf43a

Fix: 283882543
Test: atest LayoutTests#testAddingImmersiveWindow
Change-Id: I0f9f659f87222e081716c2093e187e10f7d3bdde