Fixed cts failure of WindowInsetsControllerTests

If stashing taskbar is caused IME visiblity, we could just skip updating
rounded corner insets since the rounded corners will be covered by IME
during IME is showing and task bar will be restored back to unstashed
when IME is hidden.

Bug: 225765490
Test: atest WindowInsetsControllerTests
Change-Id: If8f40add0d4d9f746169d26f46f27545b4023e90