Make eventId increment per event

Currently, eventId is incremented for each subscriber even for the same
event. So, this is to increment eventId per event.

Tested:
- Run multiple instance of event listeners
- Generate an event like
```
curl -k -H "X-Auth-Token: $bmc_token" -H "Content-Type: application/json" \
     -X POST https://${bmc}/redfish/v1/Managers/bmc/LogServices/Dump/Actions/LogService.CollectDiagnosticData \
     -d '{"DiagnosticDataType":"Manager"}'
```

- Check the EventId whether it is incremented per event
```
  "@odata.type": "#Event.v1_4_0.Event",
  "Events": [
    {
      ...
      "MessageId": "TaskEvent.1.0.3.TaskStarted",
      "MessageSeverity": "OK",
      "OriginOfCondition": "/redfish/v1/TaskService/Tasks/0",
      "Resolution": "None."
    }
  ],
  "Id": 2,      <===
  "Name": "Event Log"
}
```

Change-Id: I7a1f61cb932068cac5a50838fefeeaf880516a97
Signed-off-by: Myung Bae <myungbae@us.ibm.com>
diff --git a/redfish-core/include/event_service_manager.hpp b/redfish-core/include/event_service_manager.hpp
index 7fac1f9..ad756df 100644
--- a/redfish-core/include/event_service_manager.hpp
+++ b/redfish-core/include/event_service_manager.hpp
@@ -660,8 +660,8 @@
             std::string strMsg = msgJson.dump(
                 2, ' ', true, nlohmann::json::error_handler_t::replace);
             entry->sendEventToSubscriber(std::move(strMsg));
-            eventId++; // increment the eventId
         }
+        eventId++; // increment the eventId
     }
 };