st/nine: Disable parts of lighting calculation if no normal provided
st/nine: Disable parts of lighting calculation if no normal provided

Behaviour found in Wine sources, and checked with some test apps.

Signed-off-by: Axel Davy <2b6ef604b998fb81662f85c329e4fc020eae8e5d@ens.fr>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler