Improve frontend handling of missing data

After graph was updated with partial data (or none at all), it would
sometimes stop working even after new, complete data was given.
It doesn't seem to do that anymore.

static/js/dashboard.js

@@ -215,6 +215,12 @@ function loadData(report, callback) {
 
     getData(report.kpi, options, function(data) {
         report.series = report.dataToSeries(data);
+
+        // If any series are empty, filter them out.
+        report.series = report.series.filter(function(series) {
+            return series.data.length > 0;
+        })
+
         callback();
     });
 }
@@ -291,7 +297,12 @@ function updateGraph(report, newSeries) {
 
     // Update the graph with the new series
     report.graph.series = newSeries;
-    report.graph.update();
+    try {
+        report.graph.update();
+    } catch(e) { // Something bad happened while trying to update the graph.
+        // Draw a new graph
+        drawGraph(report, newSeries);
+    }
 }
 
 /**
@@ -326,7 +337,6 @@ function dateChanged(report) {
     }
 
     loadData(report, function() {
-        console.log(report.series);
         updateGraph(report, report.series);
     });
 }
@@ -679,6 +689,8 @@ setupSegmentControls();
             }
         }
 
+        Rickshaw.Series.zeroFill(series);
+
         return series;
     };