Solved a bug when trying to create a group with no servos.

src/dynamixel_motor_group.cpp

@@ -851,7 +851,7 @@ void CDynamixelMotorGroup::load_config(std::string &filename)
         this->set_max_torque(i,motor->max_torque());
         this->set_limit_torque(i,motor->max_torque());
       }  
-      if(this->config[0].min_angle==-this->info[0].center_angle && this->config[0].max_angle==-this->info[0].center_angle)
+      if(cfg->dyn_motor_config().size()>0 && this->config[0].min_angle==-this->info[0].center_angle && this->config[0].max_angle==-this->info[0].center_angle)
       {
         this->mode=torque_ctrl;
         for(i=1;i<this->servo_id.size();i++)