Steps to reproduce:
- Open a page for editing, chose the insert link dialog.
- Enter "a a" as url
- Chose "To an external web page" (If you ask why someone should do this, I can only say that I don't know, but that I've seen too many of these links to ignore them)
- Click "Insert Link"
Result: [http://a%20a a a] is inserted.
Expected result: The insert link button should be grayed out when the link to be inserted is definitely invalid.