Fix bug with container on Windows.

This fix the bug from:
https://github.com/ArthurSonzogni/FTXUI/pull/11

About:
~~~
Bug: Focus handling not working

in the examples (e.g. checkbox.cpp) I can toggle the individual
checkboxes but I cannot move between items, I tried to understand the
focus implementation but am I unsure which keypresses would move focus
between different components
~~~