insertElement and insertHtml fail if widget is first in editor (Chrome)

[Brandon]

Steps to reproduce

(Simple demo attached)

1. In Chrome, load editor with only a widget in it (or at least have a widget as first thing in the editor).
2. Without selecting an insert point in the editor, try using insertHtml or insertElement. You can also try inserting widget which uses insertElement method - ​https://github.com/ckeditor/ckeditor-dev/blob/master/plugins/widget/plugin.js#L420

Expected result

The HTML should be inserted before the widget.

Actual result

Fails with error "Uncaught TypeError: Cannot read property 'checkReadOnly' of undefined"

Other details (browser, OS, CKEditor version, installed plugins)

Chrome 44.0.2403.125 | Windows 10/8.1 | CKE 4.5.1 | Plugins: Widget / Enhanced Image (any plugin that uses widget will do)

[Brandon]

Demo of Problem

[Jakub Ś]

#14768 was marked as duplicate.

Problem can be reproduced from CKEditor 4.3.1 in Webkit browsers (both Safari & Chrome). In version 4.3.0 error is Cannot read property 'collapsed' of undefined

[Jakub Ś]

Similar issues with 'checkReadOnly' can also be found in: #13314, #14809