Make configurator more robust

When an array of services of a plugin is undefined, return an empty
array when getServices() is called.

app/js/arethusa.core/configurator.service.js

@@ -8,10 +8,14 @@ angular.module('arethusa.core').service('configurator', function($injector) {
   };
 
   this.getServices = function(serviceNames) {
-    var that = this;
-    return arethusaUtil.map(serviceNames, function(name) {
-      return that.getService(name);
-    });
+    if (serviceNames) {
+      var that = this;
+      return arethusaUtil.map(serviceNames, function(name) {
+        return that.getService(name);
+      });
+    } else {
+      return [];
+    }
   };
 
   // this.configuration is set from outside on page load

spec/arethusa.core/configurator.service_spec.js

@@ -30,5 +30,11 @@ describe('configurator', function() {
       expect(services).toContain(mock1);
       expect(services).toContain(mock2);
     }));
+
+    it('returns an empty array when no service names are given', inject(function(configurator) {
+      var names = undefined;
+      var services = configurator.getServices(names);
+      expect(services).toEqual([]);
+    }));
   });
 });