Links anchor appended multiple times

Steps to recreate:

• Create an external link using linkit, tinymce button, with an anchor, e.g. http://example.org/path#anchor
• Click insert and select the link again, and click the linkit button again.
• Don't change anything, instead, click insert again.
• Now you have two anchors, like http://example.org/path#anchor#anchor

I haven't got the time right now to make a patch, but i will review this later.