Fix fullscreenized images crashing OpenGL on start.
Fix fullscreenized images crashing OpenGL on start.

Wait for OpenGL first

fixes #290

OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm