fix singularity for getRPY.  need to add unit test for this particular problem.
fix singularity for getRPY.  need to add unit test for this particular problem.

robotology-dependencies/urdfdom,robotology-dependencies/urdfdom,robotology-dependencies/urdfdom,keulYSMB/urdfdom,shadow-robot/urdfdom,keulYSMB/urdfdom,keulYSMB/urdfdom,keulYSMB/urdfdom,shadow-robot/urdfdom,robotology-dependencies/urdfdom,shadow-robot/urdfdom,shadow-robot/urdfdom