KinematicsMetrics crashes when called with non-chain groups.

This change makes it so the KinematicsMetrics class returns false (failure) instead of causing exceptions to be thrown which no one catches and thus crashes your program.

The ultimate cause is that RobotState::getJacobian() does not have a proper error return value, it throws an exception instead.  That API should ultimately be changed, but this change avoids the crash with no API change and is thus less of a big deal in my opinion.