NWN: legal billboard fade with shader rendering

Properly update fade alpha when rendering legal billboard with
shader render path.

src/engines/nwn/gui/legal.cpp

@@ -73,6 +73,10 @@ class FadeModel : public Graphics::Aurora::Model_NWN {
 			hide();
 		}
 
+		for (NodeList::iterator n = _currentState->rootNodes.begin();
+		     n != _currentState->rootNodes.end(); ++n) {
+			(*n)->setAlpha(_fadeValue);
+		}
 	}
 
 public:
@@ -121,6 +125,11 @@ class FadeModel : public Graphics::Aurora::Model_NWN {
 
 		updateFade();
 	}
+
+	void renderImmediate(const glm::mat4 &parentTransform) {
+		updateFade();
+		Graphics::Aurora::Model_NWN::renderImmediate(parentTransform);
+	}
 };