This patch fixes the way `org-babel-detangle' handles false positive
matches for links.  Without the patch it tries to use match data that
may not be present in a false positive.  I've also included a regression
test.

This is my first contribution to Org Mode or Emacs and my first patch
by mailing list so please let me know if I've overlooked anything.

Also note I have not assigned copyright to FSF at this time, however I
believe this change should be small enough to not require it.

Kevin Foley