test mergemulti traj at one place

apps/function/multi_traj_functions.cpp

@@ -224,6 +224,7 @@ vector<pair<string, vector<pair<uint64_t, uint64_t>>>> crossFilter(
                 uint32_t period = it->second.second - it->second.first;
                 if(period > longestPeriod){
                     longestId = it->first;
+                    longestPeriod = period;
                 }
             }
             string currTaskPath = filteredTaskInfo[longestId].taskPath;