e_hwc_windows: check transition of client to none when display state is changed

e_hwc_windows: check transition of client to none when display state is changed

consider the case below for prevent flickering
1. 1st window is displayed by HW Plane
   2nd window is displayed by gl compositing
2. gl compositor call rendering of 2nd window but buffer is not enqueued
3. 3rd window is launched and 1st window is hidden
   2st window should be hided
4. buffer of 2 step is enqueued
5. 1nd window is unset by HW Plane because buffer of 2 step doesn't render 1st window
6. 2nd window is shown without 3rd window

Change-Id: I8307901fd70f181c009a548fc96fb34e7b17576f