Initial bounding box calculation are wrong when using nested boxes #56

I used a message and codesandbox from a discord server
https://discord.com/channels/740090768164651008/745777196911689748/860103131593310238
https://codesandbox.io/s/playing-with-react-three-flex-forked-05wo8?file=/src/App.js

The problem is that initial bounding box for a group that contains other boxes is reported incorrectly (width should be 200, but it's 100). This probably has to do with that until flex is calculated first time, boxes inside other boxes positioned in the same place