Allows cd command to go back to the root directory when 'cd \' executed in system. This change prevents last PathRemoveLastItem() call which truncates '\' from 'fs0:\' in desired root path which is required to set CWD to the root directory. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Tapan Shah <tapandshah@hpe.com> Reviewed-by: Jaben Carsey <Jaben.carsey@intel.com>