Fix small JS issue if the underlying repository has no branches defined

This allows the user to continue the setup, even if the repo is empty.

static/js/directives/ui/trigger-setup-githost.js

@@ -123,6 +123,7 @@ angular.module('quay').directive('triggerSetupGithost', function () {
 
         ApiService.listBuildTriggerSubdirs($scope.trigger['config'], params).then(function(resp) {
           if (resp['status'] == 'error') {
+            $scope.locations = [];
             callback(resp['message'] || 'Could not load Dockerfile locations');
             return;
           }