Remove Modal Backdrop

Created by: silviodelgado

After close a modal, the dispose method is triggered.

The line 117 of file backdrop.js contains:

this._getElement().parentNode.removeChild(this._element)

(This code is also on line 2633 of bootstrap.js file)

But when we handle modals manually (create and trigger dynamically),this._getElement().parentNode is null. Then, a TypeError is thrown.

Before this call (line 117 of backdrop.js file, should add an element checking (if is null).