Node: Fix display(...) crash (refine previous commit).
Node: Fix display(...) crash (refine previous commit).

Fix crash if a node's state list changes while display(...) is active. This commit introduces the same stability as the last one, while reducing the overhead. The difference to the former less robust version is now neglectable. Tested with Scene "27k Cubes with many materials".

PADrend/MinSG,PADrend/MinSG,PADrend/MinSG