Return value from check_egl_context, the current native window is invalid

We should wait until we are provided a valid window handle.

Property definitions

gamnit :: egl $ GamnitDisplay :: native_window_is_invalid=
	# Return value from `check_egl_context`, the current native window is invalid
	#
	# We should wait until we are provided a valid window handle.
	var native_window_is_invalid = false
lib/gamnit/egl.nit:139,2--142,37