fix wrong nb_ pointer inside rb_ strucutre
fix wrong nb_ pointer inside rb_ strucutre

The rb_ must be reset, so nb_ pointer must point to newly created
object.

This will fix issue in OR-1032

QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD,The-OpenROAD-Project/OpenROAD,QuantamHD/OpenROAD