Fix duplicate display update upon nav mode change

When changing the navigation mode with PiP present, PipController could
receive multiple onDisplayChanged callbacks due to insets check added in
ag/19904559, this could eventually be conflict with the
DisplayInsetsController#OnInsetsChangedListener callback.

Bug: 261388495
Test: repeatedly change nav mode and enter PiP
Test: ensure PiP window not overlap with TaskBar (when in button nav)
Change-Id: If8aeebbb26b2123f38e3abb63aa67b42aca759a8