Fix "data points outside time range" when there is no datapoints and aggregate function is used

src/datasource-zabbix/timeseries.js

@@ -103,6 +103,8 @@ function groupBy_perf(datapoints, interval, groupByCallback) {
   let point_frame_ts = frame_ts;
   let point;
 
+  if (datapoints.length > 0) {
+
     for (let i=0; i < datapoints.length; i++) {
       point = datapoints[i];
       point_frame_ts = getPointTimeFrame(point[POINT_TIMESTAMP], ms_interval);
@@ -125,6 +127,8 @@ function groupBy_perf(datapoints, interval, groupByCallback) {
     frame_value = groupByCallback(frame_values);
     grouped_series.push([frame_value, frame_ts]);
 
+  }
+
   return grouped_series;
 }