fix error

* Do not hide the loading view when collection.length === 0

```
new bbGrid.View({
        container: $('#bbGrid-clear'),
        collection: new Backbone.Collection([]),
        colModel: [
                { title: 'ID', name: 'id' },
                { title: 'Full Name', name: 'name'},
                { title: 'Company', name: 'company'},
                { title: 'Email', name: 'email' }
        ]
});
```


* Do not select the selected rows when set selectedRows values.

```
new bbGrid.View({
        container: $('#bbGrid-clear'),
        collection: new Backbone.Collection([
                {id: 1, name: 'wenzhixin', company: 'scutech', email: 'wenzhixin
        ]),
        selectedRows: [1],
        multiselect: true,
        colModel: [
                { title: 'ID', name: 'id' },
                { title: 'Full Name', name: 'name'},
                { title: 'Company', name: 'company'},
                { title: 'Email', name: 'email' }
        ]
});
```