[FCKeditor] window.opener has no properties

window.opener has no properties
imagebrowser.js (line 10)
[Break on this error] window.opener.SetUrl( fileUrl, null, null, alt ) ;

Probably only FCKeditor related.
Steps to reproduce:
- Open in FCKeditor Image Dialog box.
- Click "Browse Server" button
- Image Browser popup will show up
- Close FCKeditor Image Dialog box
- Click "Insert" in Image Browser
because the opener window has been closed, we get an error.

Theoretically this shouldn't be a problem, but if this module will be more popular (it's nice and simple, so it's just a matter of time ;-)), some people may start reporting this issue.