Accept metrics list when bytes and packet metrics are missing

In NodeConnectorStatisticsChangeHandler a TDRMetricRecord list is built with direct array[] access from the FlowCapableNodeConnectorStatistics supplied.  In some cases, a FlowCapableNodeConnectorStatistics instance is supplied without bytes and packet metrics.  This fix enables building the TSDRMetricRecord with or without the bytes and packet metrics.  It was failing when FlowCapableNodeConnectorStatistics did not supply the bytes and packet metrics.

If this effects downstream processing, then that should probably be fixed to accomodate this change.  The failing code was padding the TSDRMetricsRecord with a timestamp and no data.  If downstream needs this then we should probably fix that as there is no data associated with the timestamp.