Clicking to set cursor before first character in ContentEditable element inserts rogue character and loses focus

[AndyGCook]

There seems to be a bug when clicking directly before the first character in a ContentEditable element. After the click, the ContentEditable cursor disappears and a rogue character is inserted into the editor.

I think this has to do with trying to detach the shadow cursor in EditableCaret.prototype.getOffset method.

I'm trying to debug it and will roll in a patch if I can figure it out... just thought I'd add it as an issue here in case it's an easy fix that I'm missing.