BUG: collated format and writing of NURBS3DVolume CPs - see #1947

The if(Pstream::master()) clause in NURBS3DVolume::writeCpsInDict() was
causing the fileName of the regIOobject not to be allocated in all
processors, giving problems when masterUncollatedFileOperation::masterOp
was called by collatedFileOperation::writeObject for the mkDirOp.