[O] <<< >>> radio links should not match empty text

[Daniel Clemente]

Hi, recently this syntax: <<< >>> started highlighting all spaces (spaces 
between words) as if they were links. I see them with a blue underline.
  I found this because I used some Unicode-art like <<<<<<<<< >>>>>>>>> where I 
certainly didn't mean to define a radio link.

  This happens since this change:

#+BEGIN_QUOTE
commit 1c1936fbb1f0c42e5c7e1d3c903626aa5993a357
Author: Nicolas Goaziou <address@hidden>
Date:   Tue Mar 25 10:15:25 2014 +0100

    Allow radio links after an apostrophe and mid-word
    
    * lisp/org.el (org-make-target-link-regexp): Allow radio links after
      an apostrophe and mid-word.  Small refactoring.
    
    * testing/lisp/test-ox.el (test-org-export/resolve-radio-link): Add
      test.
    
    See http://permalink.gmane.org/gmane.emacs.orgmode/84108.
#+END_QUOTE

  Greetings,
Daniel