kiwi: Make sure Kiwi modules takes the entire space on startup

This removes a potential race on startup, where the module was
still using its original size (800x600), and does not have time
to tell the extension to resize it to maximum size.

Example trace:
```
resize! 1280/834 => JS tells Kiwi to resize
debug:(0) -2147483648 InitContext 800x600s1 => Initialized with default size
resize:1280/834 => Kiwi tells JS to resize element
status:Connecting...
debug:(2) -2147483648 message=hidpi:0
status:Connected.
connected:Version received
debug:(1) -2147483648 Asked for resolution 800x600 => Kiwi asks for wrong resolution
debug:(0) 0 fps: 0 (0) delay: -2147483648 deltat: -2147483648 target fps: 30 800x600
debug:(0) 75 InitContext 1280x834s1 => Kiwi gets notified of element resize only here
debug:(2) 100 receive (binary): R => croutonfbserver tells Kiwi 800x600 is ok
resize:800/600 => Kiwi tells JS to resize down to 800x600
debug:(0) 131 InitContext 800x600s1
```