Ensure connect device button is shown

This CL fixes a bug in the logic of attachConnectNewDeviceItemIfNeeded
that caused the "Connect a device" button to disappear after the output
device was changed, if the input routing flag is enabled.

Before:
https://screencast.googleplex.com/cast/NTU5NTQzMDEzNzEwMjMzNnw0NWY1Mzk3YS0wZA

After:
https://screencast.googleplex.com/cast/NTQwMDMwMjcyNjQxNDMzNnw2NjA3MjM4Ni02MA

Test: atest MediaSwitchingControllerTest
Bug: b/379902375
Flag: com.android.media.flags.enable_audio_input_device_routing_and_volume_control
Change-Id: Ic16f0d18a5cac7e3279bbaaabbfdb89eb7b5b2e2