Fix small issue where overflow expanded view wouldn't show

Small regression from ag/30408723; don't need to wait for taskview to
be visible if it's the overflow view.

Flag: com.android.wm.shell.enable_bubble_bar
Test: manual - navigate to bubble overflow in bar mode
Bug: 374640759
Change-Id: I4ee92263ed7373dd9e9cc356e4b6bbf8b0883635