Initial fix for T53014: Cycles material preview no light

This was introduced on 9ad2c0b615.

Although this still doesn't fix the issue, it updates the preview
system to use COLLECTION_DISABLED as intended.

What is missing now is for the flushing to work effectively.

source/blender/editors/render/render_preview.c

@@ -313,7 +313,7 @@ static void set_preview_layer(SceneLayer *scene_layer, char pr_type)
 			lc->flag = COLLECTION_VISIBLE;
 		}
 		else {
-			lc->flag = 0;
+			lc->flag = COLLECTION_DISABLED;
 		}
 	}
 }