Ensure clear state when getDestinationBounds for PiP

When request PipBoundsHandler#getDestinationBounds from different
component, simply reset any internal states.

Bug: 153349821
Test: atest PipBoundsHandlerTest
Test: atest PinnedStackTests#testAutoEnterPictureInPicture \
            PinnedStackTests#testEnterPipWithMinimalSize
Change-Id: I71a64fa169918fc0b191caf583a22f864152c2fe