Fixed bug with sumSeries() and series with 0 values.
Fixed bug with sumSeries() and series with 0 values.

xiaohuiz/grafana-zabbix,alexanderzobnin/grafana-zabbix,alexanderzobnin/grafana-zabbix,alexanderzobnin/grafana-zabbix,alexanderzobnin/grafana-zabbix,alexanderzobnin/grafana-zabbix,alexanderzobnin/grafana-zabbix,xiaohuiz/grafana-zabbix