bug: Window size is not working properly

[stabldev]

https://github.com/tokitou-san/Instagram-UI/blob/73f802c4521002509335518a036b47df7bbadb9a/main.py#L13-L15
Page width and height is not same every time we run app.
I.e: If I run app window size is correct. But If I rerun app, window size might be different ( more like full screen ).

Tracking: flet-dev/flet#1651