PM::getCurrentTimeStamp considering not initialized case

include/core/processor/processor_motion.h

@@ -170,7 +170,7 @@ class ProcessorMotion : public ProcessorBase, public IsMotion
          * \param _x the returned state vector
          */
         virtual void getCurrentState(Eigen::VectorXd& _x) const override;
-        virtual void getCurrentTimeStamp(TimeStamp& _ts) const override { _ts = getBuffer().back().ts_; }
+        virtual void getCurrentTimeStamp(TimeStamp& _ts) const override { _ts = (last_ptr_ == nullptr or getBuffer().empty() ? TimeStamp(0) : getBuffer().back().ts_); }
         using IsMotion::getCurrentState;
         using IsMotion::getCurrentTimeStamp;