Android: Mainwindow has black border in the bottom when set to full screen

User reported about black border in their app if they set it to full screen.

Qt support tested example provided and could reproduce the issue with Lenovo M10 tablet.

Steps to reproduce:

1) Start App in Landscape
2) press "change to fullscreen" button
=> Fullscreen shown but with black border
3) button text don't change to "wait 2 secs" or "Quit"
=> in our App we can't see any screen update
4) press button again => Quit => TouchEvents are recognized