Closes elastic#1720. Now pie charts with a single value for its first…

… slice and multiple values for each layer on top of that will display a llegend as intended.

src/kibana/components/vislib/lib/data.js

@@ -97,7 +97,8 @@ define(function (require) {
       _.forEach(visData, function countSeriesLength(obj) {
         var rootSeries = obj.series || (obj.slices && obj.slices.children);
         var dataLength = rootSeries ? rootSeries.length : 0;
-        var label = dataLength === 1 ? rootSeries[0].name : undefined;
+        var label = dataLength === 1 ? rootSeries[0].label || rootSeries[0].name : undefined;
+        var children = (obj.slices && obj.slices.children && obj.slices.children[0].children);
 
         if (!this.seriesLabel) {
           this.seriesLabel = label;
@@ -107,7 +108,7 @@ define(function (require) {
           sameSeriesLabel = false;
         }
 
-        if (dataLength > 1 || !sameSeriesLabel) {
+        if (dataLength > 1 || children || !sameSeriesLabel) {
           isLegend = true;
         }
       });