[Sidestage] App window incorrectly resized after fullscreen switch

[Alberto Mardegan]

Please see the attached screenshot. This happens on a M10 tablet.

To reproduce:
1) Open youtube in the browser
2) Open two apps in the sidestage; eg, twitter and telegram
3) Bring telegram in the active sidestage, above the browser
4) Start playing a video
5) Switch the video to fullscreen
6) Go to the task switcher
7) Bring twitter in the sidestage
8) close the sidestage
9) exit fullscreen mode in youtube
10) bring telegram in the sidestage

At this point, telegram's window will be cut off a few pixels in the bottom.