Only return that bubbles are on home if we actually have bubbles

This causes an issue in the touch inset calculations resulting in
taskbar items being not touchable causing some tests to fail (thank
you tests for catching this!)

Flag: com.android.wm.shell.enable_bubble_bar
Test: atest NexusLauncherTests:com.android.quickstep.TaplTestsTaskbar
Bug: 349174989
Change-Id: I8cad22be92f219e0e9d3ec0f551764681f281844