Fixed for .. of IE 11 error. (#1187)

* =fixed for of and graph null filter exception

* Simplified GetMetrics method.

src/app/backend/resource/metric/downloader.go

@@ -30,9 +30,6 @@ type MetricPromises []MetricPromise
 // In case of no metrics were downloaded it does not initialise []Metric and returns nil.
 func (self MetricPromises) GetMetrics() ([]Metric, error) {
 	result := make([]Metric, 0)
-	if len(self) == 0 {
-		return result, nil
-	}
 
 	for _, metricPromise := range self {
 		metric, err := metricPromise.GetMetric()

src/app/frontend/common/components/graph/graph_component.js

@@ -61,7 +61,8 @@ export class GraphController {
       let y1max = 1;
       let y2max = 1;
       // iterate over metrics and add them to graph display
-      for (let metric of this.metrics) {
+      for (let i = 0; i < this.metrics.length; i++) {
+        let metric = this.metrics[i];
         // don't display metric if the number of its data points is smaller than 2
         if (metric.dataPoints.length < 2) {
           continue;

src/app/frontend/common/components/graph/graphcard_component.js

@@ -29,7 +29,8 @@ export class GraphCardController {
    * @return {boolean}
    */
   shouldShowGraph() {
-    return this.metrics.filter((metric) => metric.dataPoints.length > 1).length > 0;
+    return this.metrics !== null &&
+        this.metrics.filter((metric) => metric.dataPoints.length > 1).length > 0;
   }
 }