Fix lighting of upright_sprite entities

[x2048]

The goal is to fix lighting of upright_sprite entities broken in cef252b. Upright sprite entities (icons on drawers or player entity in devtest game) would not take light of the current node into account when shaders are enabled and always be drawn in full brightness.

Example devtest player in a dark cave;

cef252b removed a call to IMeshSceneNode::setReadOnlyMaterials(true), meaning that materials in IMeshSceneNode would take precedence over the materials of its mesh buffers. GenericCAO::setNodeLight() was still using mesh buffer materials directly.

This PR changes GenericCAO::setNodeLight() to work with IMeshSceneNode materials via getMaterial() call.

To do

This PR is a Ready for Review.

How to test

1. Start devtest
2. Go underground
3. Switch camera to 3rd person mode
4. Player entity must be black due to no light nearby.

[sfan5]

LGTM