fix(pagination): avoid initial double firing of paginationChanged

When initially loading a grid with `ui.grid.pagination` enabled, **paginationChanged** is triggered two times since the watcher values transition from `undefined` to the **initial value**

Found while developing a `pageSize` feature on an alternate pagination project: michaelbromley/angularUtils#212

src/features/pagination/js/pagination.js

@@ -375,7 +375,7 @@
           var deregT = $scope.$watch('grid.options.totalItems + grid.options.paginationPageSize', setShowing);
 
           var deregP = $scope.$watch('grid.options.paginationCurrentPage + grid.options.paginationPageSize', function (newValues, oldValues) {
-              if (newValues === oldValues) {
+              if (newValues === oldValues || oldValues === undefined) {
                 return;
               }