Crash when drawing while at the same time `switchToOnscreen` is called

[sindreij]

I'm pretty sure this happens because switchToOnscreen is running while the js thread is also writing to the GPU in some way.

Fixed it by waiting on getNativeSurface to return a surface with with > 0 and height > 0

crashlog.txt

[wcandillon]

do you have a reproducible example so we can test a fix for it?