nviz: Directly call glViewport

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@72968 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/nviz/render.c

@@ -218,7 +218,7 @@ int Nviz_make_current_render_window(const struct render_window *rwin)
     wglMakeCurrent(rwin->displayId, rwin->contextId);
 #endif
 
-    GS_set_viewport(0, rwin->width, 0, rwin->height);
+    glViewport(0, 0, rwin->width, rwin->height);
 
     return 1;
 }