fix(graphite): jsonData is not always present.

public/app/plugins/datasource/graphite/config_ctrl.ts

@@ -9,6 +9,7 @@ export class GraphiteConfigCtrl {
 
   /** @ngInject */
   constructor($scope) {
+    this.current.jsonData = this.current.jsonData || {};
     this.current.jsonData.graphiteVersion = this.current.jsonData.graphiteVersion || '0.9';
   }