the R_TRANSFORMED flag enabled. Now vertex normals are properly
transformed by ObjectInstanceRen::nmat[3][3] and normalized. It is
noted that in the case of R_TRANSFORMED flat faces, surface normals
are transformed and normalized by RE_vlakren_get_normal().
The bug was reported by Stéphane Grabli via personal communication.
Thank you Stéphane for the careful code review!