Fix MovableElements during overscroll on overlays

This CL fixes a bug that would cause some MovableElement's to disappear
if they are in the current scene but not in an overlay that is currently
being overscrolled.

Bug: 353679003
Test: atest OverlayTest
Flag: com.android.systemui.scene_container
Change-Id: I4919846c260e572e1eee38e13decb4d6a1cd0e1f