If registered type returns G_TYPE_NONE, push nil.
If registered type returns G_TYPE_NONE, push nil.

This is workaround for unfortunate misuse of G_TYPE_NONE in
g_registered_type_info_get_g_type(), which should return
G_TYPE_INVALID in case of errors instead of G_TYPE_NONE (which is a
valid type, albeit nonsensical, because it represents 'void').

zevv/lgi,psychon/lgi,pavouk/lgi