Normalize point source color

See Issue CelestiaProject#2016

Pedro noted that old addons use [ 0 0 0 ] in order for object to not get rendered as points; this is handled by the condition at the beginning, which excludes such objects (and so they do not get rendered anyway).

src/celengine/render.cpp

@@ -2966,13 +2966,13 @@ void Renderer::renderPlanet(Body& body,
         }
     }
 
-    if (body.isVisibleAsPoint())
+    if (body.isVisibleAsPoint() && body.getSurface().color.toVector3().maxCoeff() > 0.0f)
     {
         renderObjectAsPoint(pos,
                             body.getRadius(),
                             appMag,
                             discSizeInPixels,
-                            body.getSurface().color,
+                            body.getSurface().color / body.getSurface().color.maxCoeff(),
                             false, false, m);
     }
 }