IE6-8 JS error thrown when pasting with dialog

[Jakub Ś]

I have found it when checking #8849 and #9127.

To reproduce:

1. Load the "replacebyclass" sample (important);
2. Select first line and copy/paste it. You should have 7 lines.
3. Select the bold text "sample text" in third line from the bottom;
4. Press Tab key to move focus outside of editor;
5. Click on "Paste" toolbar button; choose to deny clipboard access in order to bring up dialog.
6. Fill in the dialog with some text "abc" then click on Ok

Result: The above TC produces JS error:

Message: Invalid argument. Line: 938 URI: /ckeditor/_source/plugins/selection/plugin.js

It has been reproducible (IE6-8) from rev. [7239] to [7883]; got fixed and showed up again from [7447] to [7517]; got fixed and now has been reproducible from CKEditor [7560]

Guys, Please use CRTL+F5 or clear cache from time to time if you have problems with reproducing.