Hotfix: Allow t=0 to be a valid timestamp

src/common/time_stamp.cpp

@@ -37,7 +37,7 @@ TimeStamp::TimeStamp(const TimeStamp& _ts) :
 
 TimeStamp::TimeStamp(const double& _ts) :
         time_stamp_nano_(_ts > 0 ? (unsigned long int)(_ts*1e9) : 0),
-        is_valid_(_ts > 0)
+        is_valid_(_ts >= 0)
 {
     //
 }