UI: Fix topology view when you only have one switch.

src/main/resources/web/js/models/topologymodel.js

@@ -34,14 +34,20 @@ window.Topology = Backbone.Model.extend({
                 // console.log(data);
                 self.nodes = {};
                 self.links = [];
+
                 // step 1: build unique array of switch IDs
+                /* this doesn't work if there's only one switch,
+                   because there are no switch-switch links
                 _.each(data, function (l) {
                 	self.nodes[l['src-switch']] = true;
                 	self.nodes[l['dst-switch']] = true;
                 });
                 // console.log(self.nodes);
                 var nl = _.keys(self.nodes);
+                */
+                var nl = swl.pluck('id');
                 self.nodes = _.map(nl, function (n) {return {name:n}});
+
                 // step 2: build array of links in format D3 expects
                 _.each(data, function (l) {
                 	self.links.push({source:nl.indexOf(l['src-switch']),