BUG: lbfgsb optimizer could not be used in unbounded mode

LBFGSB optimizer can put lower or upper or both constrains on selective
variables. However, it also can be used in unbounded mode.

There were some issues that prevented LBFGSB to be used in unbounded
mode. This patch resolves these issues and expands the
itkLBFGSBOptimizerv4Test to check the unbounded LBFGSB too.

Change-Id: Id36b39a1fe500d449bbaee25b886ecae608355f5
Merge topic 'lbfgsbOpt_r'

24fc4fe4 BUG: lbfgsb optimizer could not be used in unbounded mode